The effect of antilymphocytic antibody on the humoral immune response in different strains of mice: III. The response to type III pneumococcus polysaccharide

The effect of a single batch of horse anti-mouse thymocyte globulin on the immune response to type III polysaccharide antigen has been investigated in 2–3-month-old male A/HeJ, C₅₇B1, BALB/c, DBA/1, CBA and C₃H mice. In almost all cases the intraperitoneal administration of 5 mg of this material on days –4 and –2 significantly suppressed the immune response to 0.1, 1.0 and 5.0 μg of antigen injected i.v. on day 0. Further studies undertaken in BALB/c mice indicated that effective suppression of the immune response to type III polysaccharide antigen could also be achieved by injecting 5 mg of this product (i.p.) some 15–30 minutes prior to antigenic challenge. Preliminary cell reconstitution studies in antilymphocytic antibody-treated CBA mice indicate that the ability to respond to type III polysaccharide can be partially restored by the injection of syngeneic thymocytes, bone marrow cells or spleen cells.     

Immunopathological aspects of Plasmodium berghei infection in five strains of mice. I. Immune complexes and other serological features during the infection.

The development of circulating immune complexes was studied in mice of the BALB/c, A/J, OF1, CBA and C57B1 strains infected with P. berghei. Complexes were evaluated in relation to levels of parasitaemia, soluble antigen, specific antibody and C3. Susceptibility to infection was greatest in BALB/c, A/J and OF/a mice. The maximum parasitaemia was 30% in CBA and 70% in all other strains. Levels of soluble antigen paralleled those of parasitaemia. Specific antibody was detected in all strains, but the titre continued to rise throughout the infection only in CBA mice. Circulating immune complexes occurred in mice of all strains from day 6; the level fell after day 9 in C57B1 whereas it was maintained in CBA mice. The development of immune complexes was associated with marked depression of C3 levels in all except CBA mice, in which a transient reduction was followed by recovery. Partial characterization of the complexes showed that IgM-containing complexes appeared earliest and reached highest levels in BALB/c mice while in CBA mice, IgM complexes were found in lesser amounts and the level fell in late infection. IgG complexes rose throughout infection in CBA and fell in later stages in BALB/c and C57B1 mice. In nude BALB/c mice, immune complexes were usually not detectable and only low levels of antibody of IgM class were produced. Differences in mortality pattern could not be related to any single serological factor.     

Influence of lipopolysaccharide on graft versus host reactivity of lipopolysaccharide-unresponsive C3H/HeJ mice.

It was initially reported that lipopolysaccharide (LPS)-unresponsive C3H/HeJ mice are refractory to LPS at the B-lymphocyte level, but more recently it has been shown that other cells are similarly unaffected. The current study was undertaken to study an in vivo LPS-modulated disease process involving macrophage-T cell interactions. Adult CBA/J and C3H/HeJ mice were used as spleen donors, and graft versus host reactions were induced in BALB/c neonates. Prior LPS treatment of CBA/J adults decreased the ability of their spleen cells to cause fatal graft versus host disease in BALB/c neonates, whereas no difference was found between injection of spleen cells from normal or LPS-treated C3H/HeJ mice. Similar results were obtained with these cell types when the mouse spleen mixed leukocyte culture system was used. In a carbon clearance assay for stimulation of the reticuloendothelial system with LPS, it was found that the rate of phagocytosis was significantly increased in BALB/c and CBA/J mice 72 h after inoculation of LPS. No stimulation was seen in rate of carbon uptake in the C3H/HeJ animals after treatment with phenol-extracted LPS or with butanol-extracted LPS. An LPS-induced protective serum factor was produced only in the LPS-responsive CBA/J mice and was specific for the syngeneic cells.     

Immunity Parameters in Mice of Different Strains

Quantitative composition and functional activity of immunocompetent cells differ in mice of different strains. The counts of T cells in the bone marrow and spleen, proliferative activity of T cells in the spleen, levels of IL-2 and IL-10 production by splenic T cells, number of antigen-specific T cells and their functional activity are low in C57Bl/6, BALB/c, and CC57W mice and high in CBA/CaLac, DBA/2, and C3H animals. Low phagocytic activity of peritoneal macrophages was detected in BALB/c and CC57W mice and high activity in C3H animals. The content of antibody-producing cells in the spleens of C57Bl/6, BALB/c, and CC57W mice is higher than in CBA/CaLac, DBA/2, C3H, A/SN, and AKR/JY mice. Functional activity of B cells is lower in BALB/c and CC57W compared to CBA/CaLac and DBA/2 mice. __________ Translated from Byulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 140, No. 8, pp. 189–191, August, 2005     

Immunopathological aspects of Plasmodium berghei infection in five strains of mice. II. Immunopathology of cerebral and other tissue lesions during the infection.

Histological changes during the course of P. berghei infection were investigated in A/J, BALB/c, OF1, CBA and C57B1 mice. The findings were studied in relation to serological aspects (Contreras et al., 1980). High mortality and acute deaths occurred in A/J, BALB/c and OF1 mice and marked cerebral lesions were found in these strains from day 15, including congestion of meningeal and cerebral veins and capillaries, blocking of these vessels by heavily parasitized RBC, cerebral oedema and haemorrhages. Such lesions were minimal in CBA and C57B1 mice, and absent in mice examined 21 and 24 days after infection. Small deposits of IgG and traces of C3 were detected by immunofluorescence in the choroid plexus of most mice from day 9. Renal lesions included congestion, plugging of veins and capillaries, low-grade mononuclear infiltration and mesangial thickening; these changes were most marked in CBA, C57B1 and A/J mice. Glomerular deposits of IgM were present in all strains in the first week of infection. IgG and C3 were detected in the second week, but only traces were found in CBA mice. The livers showed congestion, accumulation of pigment in swollen Kupffer cells and mononuclear portal infiltration; these were most pronounced in A/J mice. In the spleen, there was a great increase in the reticuloendothelial cell population, white pulp proliferation, congestion and accumulation of pigment and plasma cell reaction; the pattern of white pulp expansion varied in the different strains. The results suggest that cerebral lesions play a significant role in the aetiology of acute deaths in this malaria model.     

Accelerated Skin Graft Rejection Following Transfer of Cells Sensitized to a “Weak” Histocompatibility Antigen(s)

C3H/HeJ mice were immunized with either CBA/J or C57L/J skin grafts and then tested for secondary responses against both strains. Secondary responses were measured by six-day graft rejection, ability of syngeneic spleen cells to transfer skin-graft imnunity to sublethally irradiated mice, and graft-versus-host disease (GVHD) in lethally irradiated CBA/J mice receiving C3H/HeJ spleen cells. Although failure to transfer a primary response against “Creak” histocompatibility antigens with syngeneic spleen cells was noted, the secondary responses demonstrated a cross-reacting antigen(s) which seems to be of greater imnunologic strength than the postulated H-13 difference. Possible explanations for this finding include the existence of multiple undescribed loci with cross-reacting alleles, or an increase in immunogenicity of “weak” transplantation antigens when acting in concert with “stronger” antigens.     

Failure to transfer haemolytic anaemia or glomerulonephritis with cell-free material from NZB mice

Experiments attempting to transfer haemolytic anaemia and glomerulonephritis from New Zealand Black (NZB) mice to unrelated strains by the inoculation of newborn animals with cell-free extracts of NZB tissues have been carried out. Cell-free extracts of spleen or plasma from forty-eight NZB donors were inoculated into 274 recipients of the HI, CBA, BALB/c or C57BL strains. No evidence of transfer was obtained. Transient weak positive antiglobulin tests and traces of albuminuria occurred in both inoculated and control mice. Histological examination at 12–24 months of age showed moderate to severe damage in the kidneys of occasional control and inoculated C57BL and HI mice, and mild damage in occasional control and inoculated BALB/c and CBA recipients. Electron microscopic studies of spleens and kidneys revealed a few virus-like particles in two out of eight recipients and one out of four control mice.     

Characterization of host CD4+ T lymphocytes in mice neonatally tolerized to alloantigens

BALB/c mice injected at birth with semi-allogeneic F1 spleen cells become tolerant to alloantigens as shown by their CTL unresponsiveness to the corresponding alloantigen and the persistence of donor F1 cells into the BALB/c host. Moreover, these mice develop a transient systemic lupus erythematosis-like autoimmune syndrome characterized by splenomegaly, glomerulonephritis, thrombocytopenia and abnormal serological findings, such as several autoantibodies and IgG1 hypergammaglobulinemia. Recent studies done in our laboratory have shown that donor F1 B cells persisting in the host are responsible for the production of autoantibodies and must be activated in vivo by the host CD4⁺ T lymphocytes in a MHC class II-restricted fashion. In the present work, we have focused our attention on the ability of splenic CD4⁺ T cells recovered at different periods from BALB/c mice injected at birth with (CBA/Ca × BALB. Igh^b) Fl spleen cells to interact with and activate F1 semi-allogeneic spleen cells in vitro. We show that (i) only CD4⁺ T cells from 2- and 3-week-old tolerant BALB/c mice preferentially produce IL-4 and IL-5 in response to a F1 semi-allogeneic in vitro stimulation, (ii) CD4⁺ T cells purified from 3-week-old tolerant BALB/c mice are able to induce in vitro IgG and IgM production by F1 B cells. Taken together, these results strongly suggest that host CD4+ T cells, belonging to the TH2 subset progressively lose their reactivity towards the F1 semi-allogeneic persistent B cells, reaching a state of unresponsiveness that correlates with the disappearance of serum autoantibodies and autoimmune pathology.     

Protection of newborn mice from graft versus host disease by maternal pre-immunization

Alloimmunization of BALB/c (H-2d) female mice with allogeneic spleen cells from C57BL/6 (H-2b) or CBA/H (H-2k) mice protects BALB/c offspring from graft-versus-host disease (GVH-D) following neonatal intraperitoneal inoculation of high doses of spleen cells respectively of C57BL/6 or CBA/H strains of mice. The mice survived GVH-D over one year after the allogeneic inoculum 24-48 h after birth and they did not show any signs of GVH reaction nor splenomegaly. We show that this phenomenon is antibody mediated and affects the developing immune system of the foetus. Repeated immunization of virgin female BALB/c with anti-H-2b or anti-H-2k antisera (Ab1) can equally abrogate GVH-D in their newborn offspring challenged at 24-48 h after birth with allogeneic spleen cells of H-2b or H-2k phenotype. Our results demonstrate that protection from GVH-D is not specific to the immunizing strain and occurs when the neonatal mice are challenged with C57BL/6 or CBA/H spleen cells. There is thus crossreactivity of tolerance against H-2 specificities. In this study we also report on the in vitro cellular immune responses of the surviving GVH-resistant mice and demonstrate that these responses against both the challenge and third party lymphocytes are impaired.     

Reduction of graft-versus-host disease in neonatal F1 hybrid mice.

Pre-immunization of BALB/c (H-2d) mothers with C57BL/10 (H-2b) or CBA/H (H-2k) spleen cells partially protected the F1 hybrid offspring of (BALB/c x C57BL/10) or (BALB/c x CBA/H) matings from graft-versus-host-disease (GVHD) induced by neonatal intraperitoneal inoculation with spleen cells of the paternal strain. The effects achieved were manifest as a reduction in mortality. Experiments to establish whether the phenomenon was antibody mediated were performed by passive pre-immunization of BALB/c mothers with alloantisera obtained from BALB/c previously immunized with C57BL/10 spleen cells. Alloantisera produced an equivalent reduction in GVHD mortality. Some of the F1 mice that survived challenge with paternal strain spleen cells were proven to be haemopoietic chimaeras using immunofluorescence with anti-MHC monoclonal antibodies and polymorphism of the enzyme glucose-phosphate-isomerase present in the strains used. The possible mechanisms of protection from GVHD in our mouse model are discussed.     

The role of macrophage activation and of Bcg-encoded macrophage function(s) in the control of Mycobacterium avium infection in mice.

Following the intraperitoneal inoculation of 2.5 x 10(8) colony-forming units of Mycobacterium avium strain ATCC 25291, there was bacillary growth in the liver, spleen and peritoneal cavity of C57BL/6, C57BL/10, DBA/1 and BALB/c mice whereas DBA/2, C3H/He, CBA/Ca and CD-1 mice controlled the infection showing constant or slightly decreasing numbers of viable bacteria in the liver and spleen and effective clearance of the bacilli from the peritoneal cavities. The acquisition of non-specific resistance (NSR) to Listeria monocytogenes during the infection by M. avium was high in C57BL/6, BALB/c and C3H/He mice and negligible in DBA/2 and CD-1 mice. The magnitude of the acquisition of NSR was reduced in T cell-deficient mice and was directly proportional to the dose of the inoculum of M. avium. The production of hydrogen peroxide by phorbol myristate acetate-stimulated peritoneal macrophages of M. avium-infected mice was higher in C57BL/6 and BALB/c mice than in CD-1, DBA/2 and C3H/He animals. BALB/c. Bcgr (C.D2) mice, unlike their congenic strain BALB/c, restricted bacterial growth following the intravenous inoculation of 2.5 x 10(8) CFU of M. avium as efficiently as DBA/2 mice. C.D2 and BALB/c peritoneal macrophages from infected mice produced similar amounts of H2O2 but BALB/c mice developed higher levels of NSR to listeria than C.D2 mice. The production of nitrite by peritoneal macrophages from infected mice was found to be enhanced in DBA/2 and C3H/He but not in BALB/c, C57BL/6, DC-1 and C.D2 mice. Resident peritoneal macrophages from C.D2 mice were more bacteriostatic in vitro for M. avium than macrophages from BALB/c mice. The same relative differences between the two macrophage populations were observed when the cells were activated with lymphokines. The results show that the populations were observed when the cells were activated with lymphokines. The results show that the resistance to M. avium infection in mice is under the control of the Bcg gene and that susceptibility may be due to some defect in macrophage antibacterial function not completely overcome by the activation of this phagocyte in the susceptible strains of mice.     

Stress-Triggered Abortion in Mice Prevented by Alloimmunization

PROBLEM: To determine if immunotherapy can prevent abortion triggered by mechanisms that in humans may be treatable by psychotherapy. METHOD: The effects of alloimmunization against paternal strain antigens were tested in pregnant mice subjected to stress. RESULTS: Restraint stress boosted the resorption rate assessed on day 13.5 of pregnancy in DBA/2-mated C3H/HeJ mice with an optimal effect on day 4.5 of pregnancy, and premating alloimmunization greatly reduced the effect. By contrast, CBA/J and A/J mice proved resistant to abortion boosting by restraint stress. A/J mice mated to DBA/2 or C3H/HeJ males showed reduced fertility, perhaps due to failure of pregnancy immediately after the stress, but this was not corrected by alloimmunization with either DBA/2 [class I + class II major histocompatibility complex (MHC) immunogen] or C3H/HeJ (class I MHC immunogen) splenocytes. There was a reduction in the endogenous resorption rate, however, and implantation number was slightly increased by preimmunization using DBA/2 cells. The abortion rate could be boosted, however, by ultrasonic noise stress of high abortion rate CBA/J, and preimmunization using BALB/c (H-2^d) splenocytes protected. A similar boosting of loss in low abortion rate BALB/k mice was ameliorated (albeit not completely) by preimmunization with allogeneic paternal but not syngeneic splenocytes. CONCLUSIONS: Immunotherapy may protect against a variety of potential triggers of spontaneous abortion, including those that may be amenable to psychological remedies, and possible mechanisms are discussed.     

Lipopolysaccharide from Brucella abortus behaves as a T-cell-independent type 1 carrier in murine antigen-specific antibody responses.

In order to determine the carrier nature of lipopolysaccharide from Brucella abortus (LPS-BA) in evoking humoral responses, normal and immunodeficient mice were immunized with trinitrophenyl (TNP)-conjugated LPS-BA (TNP-LPS-BA) and the responses were compared with those to known T-dependent and T-independent antigens. TNP-LPS-BA, like T-independent type 1 (TI-1) antigens such as TNP-BA and TNP-LPS from Escherichia coli (TNP-LPS-EC), generated anti-TNP responses in BALB/c, athymic BALB/c nu/nu, and CBA/N mice. In contrast, N-2,4-dinitrophenyl-beta-alanylglycylglycyl-substituted keyhole limpet hemocyanin, a typical T-dependent antigen, was not immunogenic in athymic mice, and TNP-Ficoll (T-independent type 2) was ineffective in eliciting humoral responses in CBA/N mice. These results indicate that LPS from B. abortus acts as a TI-1 carrier in generating antibody responses. In C3H/HeJ mice, TNP-LPS-BA generated higher-titer immunoglobulin G1 (IgG1), IgG2a, and IgG2b anti-TNP antibodies than TNP-LPS-EC. Compared with those from BALB/c mice, pure resting B cells isolated from C3H/HeJ mice exhibited a 30-fold lower proliferative response to LPS-EC, whereas the LPS-BA response was reduced to a lesser extent (5-fold). This suggests that the disparity observed in antibody titers was due to different abilities of LPS from B. abortus and E. coli to stimulate C3H/HeJ B cells. The ability of LPS from B. abortus to act as a carrier in generating humoral immune responses indicates that LPS-BA can be substituted for whole B. abortus organisms in vaccine development.     

Strain-dependent protective effect of adult thymectomy on murine infection by Mycobacterium lepraemurium.

C57BL/6, DBA/2, BALB/c and CBA mice were thymectomized as adults, or sham-thymectomized, and infected subcutaneously with 10(6) MLM. The number of MLM in the spleen and in the inoculated footpad was measured after 1 year of infection as well as the DTH reactions and the IgM and IgG antibody levels to MLM. Non-thymectomized mice exhibited a broad spectrum of resistance to MLM infection and of T cell mediated immunity grading from the highly resistant C57BL/6 strain to the highly susceptible CBA strain. In between, DBA/2 was found more resistant than BALB/c mice. Adult thymectomy reduced by 100 times the MLM number in the spleen of infected DBA/2 mice, without affecting that measured in the inoculated footpad, and significantly decreased DTH reaction in the same strain. No effect of adult thymectomy was observed in any other strain, except for an increase of anti MLM antibodies in BALB/c mice. These results may suggest that the medium-resistant DBA/2 strain develops after MLM infection suppressor T cells which favour MLM dissemination and are sensitive to adult.     

Antibody Production,Anaphylactic Signs,and T-Cell Responses Induced by Oral Sensitization With Ovalbumin in BALB/c and C3H/HeOuJ Mice

PurposeTwo mouse strains, BALB/c and C3H/HeOuJ, broadly used in the field of food allergy, were compared for the evaluation of the allergenic potential of ovalbumin (OVA).MethodsSensitization was made by administering 2 different OVA doses (1 and 5 mg), with cholera toxin as Th2-polarizing adjuvant. Antibody levels, severity of anaphylaxis, and Th1 and Th2 responses induced by the allergen were assessed. In addition, because the mice selected had functional toll-like receptor 4, the influence of contamination with lipopolysaccharide (LPS) on the immunostimulating capacity of OVA on spleen cells was also evaluated.ResultsBoth strains exhibited similar susceptibility to OVA sensitization. The 2 protein doses generated similar OVA-specific IgE and IgG1 levels in both strains, whereas C3H/HeOuJ mice produced significantly more IgG2a. Oral challenge provoked more severe manifestations in C3H/HeOuJ mice as indicated by the drop in body temperature and the severity of the anaphylactic scores. Stimulation of splenocytes with OVA led to significantly higher levels of Th2 and Th1 cytokines in BALB/c, and these were less affected by protein contamination with LPS.ConclusionsThe antibody and cytokine levels induced by OVA in BALB/c mice and the observation that BALB/c spleen cell cultures were more resistant than those of C3H/HeOuJ mice to the stimulus of LPS make this strain prone to exhibit Th2-mediated food allergic reactions and very adequate for the study of the features of OVA that make it allergenic.     

Characteristics of the T-dependent alpha(1 leads to 6) glucosyl (dextran) antibody response induced in mice with isomaltohexaose coupled to chicken gamma-globulin.

Isomaltohexaose flavazole coupled to chicken gamma-globulin (IM6-CGG) induced T cell-dependent anti-alpha(1 leads to 6) dextran-specific IgM and IgG responses in CBA, BALB/c and A strain mice. The IgG responses were of restricted heterogeneity as judged by isoelectric focusing, and belonged mostly to the IgG1 subclass with a minor IgG3 component in the case of BALB/c and CBA mice. All four subclasses of IgG were produced in A strain mice. In contrast, native dextran B 512 induces exclusively T cell-independent IgM responses of the same specificity for all 3 strains. All BALB/c mice immunized with different doses of IM6-CGG either in Freund's adjuvant or with Al(OH)3 plus Bordetella pertussis showed the same spectrotypes by isoelectric focusing. Sera obtained at different times after immunization of BALB/c mice failed to show spectrotype variations. Late, but not early, bleedings from CBA mice showed a tendency towards more uniform isoelectric focusing patterns.     

Weak Graft-Versus-Host Response of CBA Lymphocytes Against the H-2-Identical Strain C3H

Lymphocytes from CBA and C3H mice were tested for graft-versus-host (GVH) reactivity in C3H × CBA recipients. Three different GVH assays were used, namely, the spleen enlargement test, the popliteal lymph node assay, and inhibition of allogeneic bone marrow proliferation CBA lymphocytes showed only weak reactivity against C3H X CBA tissues in all these tests, while there was strong reactivity in H-2-different F₁ hybrids. The capacity of C3H and CBA cells in producing a host-versus-graft (HVG) reaction was also tested. It was observed that CBA cells injected into the foot pads of C₃H mice induced an enlargement of the local popliteal lymph node that was as great as when C3H cells were injected into CBA mice. On the other hand, cells from the H-2-different strain 57B1 induced a considerably smaller HVG reaition when injected into CBA mice. It is concluded that antigens that strongly stimulate mixed lymphocyte cultures do not always stimulate allogeneic lymphocytes to strong GVH reactions in vivo.     

Alpha-fetoprotein levels in different strains of mice during development.

The levels of alpha-fetoprotein (AFP) were measured at birth and at 7 days of age in plasma from Q, C3H/He-mg/Crc, BALB/c/Crc, A/Crc, CBA/Ca/Crc and C57BL/Mcl mice, and in adult blood samples and amniotic fluid at 14 days' gestation from Q, C3H and BALB/c mice. The AFP levels in amniotic fluid and neonatal plasma were significantly higher in BALB/c mice than in the other strains tested, but by postnatal day 7, C57BL and C3H mice had the highest plasma levels. It seems therefore that the genetic mechanisms controlling the synthesis of AFP prenatally may be distinct from those concerned with its reduction after birth. At 6 weeks of age the level in C3H mice was somewhat higher than in BALB/c, and more than double that in Q mice. An attempt to increase AFP levels in response to galactosamine-induced liver damage was successful only in Q adult mice. When amniotic fluids and day 0 plasma from several strains of mice were tested by polyacrylamide gel electrophoresis, no differences in AFP mobility were detected. Preliminary studies were also carried out to see if the administration of sodium butyrate, claimed to delay the timing of the fetal to adult haemoglobin switch in some mammalian species, could also affect the rate of synthesis of AFP during fetal life.     

T-helper-cell cytokines in the early evolution of murine Lyme arthritis.

Genetic susceptibility to murine Lyme arthritis has been correlated with the dominance of T-helper (Th1)- or Th2-cell-associated cytokines. To determine when commitment of the Th cell phenotype occurs, we examined the kinetics of gamma interferon (IFN-gamma) and interleukin-4 (IL-4) production by lymph node T cells of disease-susceptible C3H/HeN and disease-resistant BALB/c mice from days 2 through 30 of infection, a period encompassing the evolution of disease and early regression. BALB/c mice produced more IFN-gamma on day 2 of infection than did C3H/HeN mice, whereas IL-4 was first detected on day 14. In contrast, only IFN-gamma could be detected in C3H/HeN mice, and the levels steadily increased from day 2 to surpass those seen in BALB/c mice by day 14 of infection. Despite the difference in cytokine profiles, both BALB/c and C3H/HeN mice developed comparable arthritis assessed at 14 days of infection. Arthritis regressed by day 30 in BALB/c mice but persisted in C3H/HeN mice. These studies are the first to demonstrate that the Th2 response to Borrelia burgdorferi infection of BALB/c mice is preceded by a Th1 cytokine response. Moreover, the timing of the appearance of IL-4 suggests that its primary effect is not in preventing disease, as suggested by others, but, rather, in hastening the resolution of inflammation. The implications of these findings for the orchestration of host defense against B. burgdorferi infection are discussed.     

A novel and effective approach of developing aggressive experimental autoimmune gastritis in neonatal thymectomized BALB/c mouse by polyinosinic:polycytidylic acid

Neonatal thymectomy induces autoimmune gastritis (AIG) in 40-70% of BALB/c mice. We presumed that induction of autoimmunity by polyinosinic:polycytidylic acid (poly I:C) might allow development of a more aggressive model of AIG. A group of BALB/c mice were thymectomized on day 3 after birth. Neonatal thymectomized mice were either injected with poly I:C or phosphate-buffered saline (PBS). Non thymectomized neonatal BALB/c mice were injected with only poly I:C. All neonatal thymectomized mice injected with poly I:C developed 3 cardinal features of AIG: (1) moderate to severe degree gastritis (2) presence of autoantibody to H(+)/K(+) ATPase and (3) loss of parietal cells. However, only 70% of the PBS-treated neonatal thymectomized BALB/c mice developed some, but not, all features of AIG. A mild degree of AIG was seen in 12 of 31 nonthymectomized BALB/c mice administered with only poly I:C. Administration of poly I:C in neonatal thymectomized BALB/c mice in the first and second week appeared to be the most effective for induction of aggressive AIG. The levels of interleukin (IL)-6, IL-12p70, interferon-gamma and tumour necrosis factor-alpha were significantly higher in poly I:C-injected thymectomized mice compared to PBS-injected neonatal thymectomized mice (P < 0.05). The frequencies of CD4(+)CD25(+) regulatory T cells in the spleen were significantly decreased in neonatal thymectomized mice administered with poly I:C compared to PBS-treated neonatal thymectomized mice (P < 0.01). Taken together, these results suggest that induction of inflammatory cytokines and reduction of regulatory T cells by poly I:C might contribute to the development of an aggressive model of AIG in neonatal thymectomized BALB/c mice.