Differences in the kinetics of T cell accumulations in C3H/HeN (Bcg-resistant) and C57BL/6 (Bcg-susceptible) mice infected with Mycobacterium paratuberculosis

The accumulation of various T cell subsets in Bcg-susceptible (C57BL/6) and- resistant (C3H/HeN) strains of mice were compared following an intraperitoneal infection with Mycobacterium paratuberculosis. Groups of mice from both strains were killed at 3, 5, 10, 15, 30, and 150 days after infection and lymphocytes were harvested from the peritoneal exudate cells (PEC), spleen, intestinal epithelial lymphocytes (IEL), lamina propria lymphocytes (LPL), Peyer's patches, and mesenteric lymph node (MLN) and labelled with monoclonal antibodies to CD3, CD4, CD8, gamma delta TCR, CD25, and CD44 for flow cytometric analysis. Uninfected C3H/HeN mice had higher proportions of CD4+ cells in the spleen, MLN, LPL, IEL, and Peyer's patches, while uninfected C57BL/6 mice had higher proportions of CD8+ and/or gamma delta T cells. Significant increases in accumulation of CD8+ and gamma delta T cells were detected in the peritoneum and other tissues in both strains of mice after infection. Higher CD4/CD8 ratios were observed in most lymphoid tissues of C3H/HeN mice, while increased proportions of CD8+ and/or gamma delta T cells were present in C57BL/6 mice. These results indicate that significant differences in T cell profiles exist between these two strains of mice, both inherently and in response to infection with M. paratuberculosis. Innately lower levels of CD4+ cells and/or higher percentages of CD8+ and gamma delta T cells may play a role in the increased suspectibility of C57BL/6 mice to infection with M. paratuberculosis.     

Immunity to Cryptosporidium muris infection in mice is expressed through gut CD4+ intraepithelial lymphocytes

The role of gut intraepithelial lymphocytes (IEL) in immunity to cryptosporidial infection was investigated with a murine infection model involving Cryptosporidium muris. Oocyst shedding was monitored in severe combined immunodeficiency (SCID) mice infected with C. muris following intravenous injection of mesenteric lymph node (MLN) cells or intestinal IEL from BALB/c donor mice which were naive or previously infected with C. muris. SCID mice receiving no lymphoid cells developed chronic infections and excreted large numbers of oocysts until the end of the experiment. SCID mice injected with IEL from immune animals, however, were able to overcome the infection, and furthermore, these animals produced fewer oocysts and recovered sooner than ones which received IEL or MLN cells from naive BALB/c donors. Similar levels of protection were obtained in SCID mice injected with either 2 X 10(6) IEL or MLN cells from immune donor mice. Depletion of CD4+ cells from immune IEL, however, abrogated the ability to transfer immunity to SCID mice, while depletion of CD8+ cells only marginally reduced the protective capacity of immune IEL. Finally, control SCID mice which received no lymphocytes had < or = 1% CD4+ cells in the IEL from the small intestine, whereas the IEL from SCID mice recovered from infection, as a result of injection with immune IEL, contained 15% CD4+ cells. Thus, the ability to control C. muris infection correlated with the presence of the protective CD4+ cells in the gut epithelium.     

Mucosal immunodeficiency in HIV/SIV infection

The gastrointestinal tract is one of the major target organs for secondary infections and malignancies in HIV infection in humans indicating disturbed local immunologic defense mechanisms. Immunohistology and flow cytometric studies have demonstrated a more pronounced loss of CD4+ T cells in the intestinal mucosa compared to the peripheral blood in humans infected with HIV. In parallel, activated CD8+ T cells in the lamina propria are increased in this compartment. In SIV-infected nonhuman primates a very early loss of CD4+ T cells in the intestinal mucosa compared to the peripheral blood occurs already at 2 weeks after infection. Depletion and functional impairment of mucosal CD4+ T lymphocytes with consecutive altered cytokine secretion in HIV/SIV infection may explain the breakdown of the mucosal immune barrier leading to secondary opportunistic or nonopportunistic infections and secondary malignancies. In addition, due to the interrelation between the mucosal immune system and epithelium, these changes might be responsible for the partial small intestinal mucosal atrophy and maturational defects in enterocytes observed in HIV-infected patients.     

Activation of T lymphocytes by syngeneic murine intestinal smooth muscle cells

BACKGROUND & AIMS: Intestinal smooth muscle cells (ISMCs) express major histocompatibility complex II (MCH II) and intercellular adhesion molecule 1 (ICAM-1) after exposure to interferon gamma (IFN-gamma). T lymphocytes invade the intestinal musculature during Crohn's disease or pseudoobstruction. The aim of this study was to determine whether ISMCs activate syngeneic T cells via MHC II and ICAM-1. METHODS: Cultured murine ISMCs were exposed to IFN-gamma for 72 hours and analyzed for Mac-1 (CD11B CD18) antigen, MHC II, and ICAM-1 expression using enzyme-linked immunosorbent assay and fluorescence-activated cell sorter scan. T lymphocytes from mesenteric lymph nodes of ovalbumin-sensitized mice were examined for their ability to proliferate after coculture with IFN-gamma-pretreated and ovalbumin-pretreated ISMCs using [3H]thymidine incorporation. RESULTS: ISMCs expressed smooth muscle alpha-actin before and after IFN-gamma exposure. No macrophages were identified in these cultures. Exposure to IFN-gamma and ovalbumin for 72 hours induced MHC II and ICAM-1 expression; these treated ISMCs induced T-cell proliferation, whereas untreated ISMCs did not. T-cell proliferation was markedly enhanced by adding interleukin 2 and was blocked by antibodies against MHC II and ICAM-1. CONCLUSIONS: ISMCs activate T lymphocytes in an MHC II-linked manner and thus possess the ability to modulate immune function in the gut.     

Diverse host responses and outcomes following simian immunodeficiency virus SIVmac239 infection in sooty mangabeys and rhesus macaques

Sooty mangabeys naturally infected with simian immunodeficiency virus (SIV) do not develop immunodeficiency despite the presence of viral loads of 10(5) to 10(7) RNA copies/ml. To investigate the basis of apathogenic SIV infection in sooty mangabeys, three sooty mangabeys and three rhesus macaques were inoculated intravenously with SIVmac239 and evaluated longitudinally for 1 year. SIVmac239 infection of sooty mangabeys resulted in 2- to 4-log-lower viral loads than in macaques and did not reproduce the high viral loads observed in natural SIVsmm infection. During acute SIV infection, polyclonal cytotoxic T-lymphocyte (CTL) activity coincident with decline in peak plasma viremia was observed in both macaques and mangabeys; 8 to 20 weeks later, CTL activity declined in the macaques but was sustained and broadly directed in the mangabeys. Neutralizing antibodies to SIVmac239 were detected in the macaques but not the mangabeys. Differences in expression of CD38 on CD8(+) T lymphocytes or in the percentage of naive phenotype T cells expressing CD45RA and CD62L-selection did not correlate with development of AIDS in rhesus macaques. In macaques, the proportion of CD4(+) T lymphocytes expressing CD25 declined during SIV infection, while in mangabeys, CD25-expressing CD4(+) T lymphocytes increased. Longitudinal evaluation of cytokine secretion by flow cytometric analysis of unstimulated lymphocytes revealed elevation of interleukin-2 and gamma interferon in a macaque and only interleukin-10 in a concurrently infected mangabey during acute SIV infection. Differences in host responses following experimental SIVmac239 infection may be associated with the divergent outcome in sooty mangabeys and rhesus macaques.     

CD8 dimer usage on alpha beta and gama delta T lymphocytes from equine lymphoid tissues

Eight murine monoclonal antibodies (mAb) were used to identify the equine CD8 alpha or CD8 beta chains and to define the expression of these chains on lymphocytes from various lymphoid tissues. CD8 alpha was a 39 kDa protein and CD8 beta was a 32 kDa protein. Both chains were expressed on most of the CD8+ T lymphocytes in the peripheral blood, spleen, thymus, mesenteric lymph nodes and ileal intraepithelial lymphocytes (IEL), however, in each lymphoid compartment a percentage of lymphocytes expressed only the CD8 alpha chain. The largest percentage of CD8 alpha alpha expressing T lymphocytes was 37.7% of the IELs. Purified T lymphocytes from the ileum expressing CD8 alpha beta co-expressed the alpha beta T cell receptor (TCR). In contrast, purified CD8+ T lymphocytes from the PBMC co-expressed either the alpha beta or gamma delta TCR by RT-PCR. Use of pooled anti-CD8 alpha mAb of the murine IgG2a isotype and rabbit complement resulted in lysis of the entire CD8 expressing population in peripheral blood mononuclear cells (PBMC). These results indicated that CD8 dimer usage by equine T lymphocytes is similar to other species and that the mAb described can be further used to separate equine CD8+ T lymphocyte subsets from the lymphoid tissues to define their function in protection against viral and other infections.     

Protein deficiency induces alterations in the distribution of T-cell subsets in experimental pulmonary tuberculosis

Previous research has suggested that dietary protein deficiency alters resistance to experimental pulmonary tuberculosis, in part, by affecting the distribution and trafficking of antigen-reactive T cells. In this study, guinea pigs were maintained on either a protein-deficient (10% ovalbumin) or control (30% ovalbumin) diet and infected 4 to 6 weeks later with a low dose of virulent Mycobacterium tuberculosis H37Rv by the respiratory route. Monoclonal antibodies directed against the CD4 or CD8 markers on guinea pig lymphocytes were used in a flow cytofluorometric assay to determine the proportion of each subset in the peripheral circulation, spleen, and bronchotracheal lymph nodes at 4 weeks after infection. In uninfected guinea pigs, only the spleen exhibited an effect of diet on T-cell distribution, with small but consistent reductions in the proportions of both CD4 and CD8 T lymphocytes. However, following infection, protein deficiency exerted a profound effect on T-cell distribution. Malnourished, tuberculous guinea pigs harbored only 20 and 60% of the T cells (as a proportion of total lymphoid cells) found in the spleen and blood, respectively, of their well-nourished counterparts. Normal relative proportions of CD4 and CD8 cells were observed, however. In striking contrast, the bronchotracheal lymph nodes of protein-deprived guinea pigs with tuberculosis contained more than twice the numbers of T cells of control guinea pigs, and the normal CD4-to-CD8 ratio was reversed. Peripheral T-cell function, as measured by the delayed hypersensitivity skin test to tuberculin, and antigen-induced lymphoproliferation in vitro were markedly suppressed in protein-malnourished animals. Conversely, purified protein derivative-induced (but not concanavalin A-induced) proliferation was significantly enhanced in cultures of lymph node cells from protein-deprived tuberculous animals. Taken together, these results suggest that immunological abnormalities and loss of antimycobacterial resistance in the lungs of protein-deficient guinea pigs may be explained, in part, by sequestration of antigen-reactive T cells in the lymph nodes draining the site of infection.     

Distribution of antigen specific memory T cells in lymph nodes after immunization at peripheral or mucosal sites

The distribution of antigen-specific memory T cells in different lymph nodes of sheep was determined using an antigen-specific in vitro proliferation assay. Lymph nodes were collected from sheep immunized simultaneously with avidin or ovalbumin in a peripheral tissue site (hind leg muscle) and keyhole limpet haemocyanin (KLH) in an intestinal tissue site (gut wall or colonic mucosa). The results showed a consistently high proliferative response in typical peripheral lymph nodes (popliteal and prescapular) and a low or negative response in gastrointestinal lymph nodes (abomasal and jejunal) while the response in other nodes was variable. The low proliferative response in the gastrointestinal lymph nodes was not due to the presence of suppressor CD8- lymphocytes and the proliferative response could not be raised to peripheral lymph nodes levels with the addition to cultures of IL-2 or mitomycin-C treated peripheral lymph node cells. The high proliferative response in the peripheral lymph nodes was not suppressed by the addition of mitomycin-C-treated gastric lymph node cells but was dramatically reduced by the addition of mAb against the IL-2-receptor or by depletion of CD4- T cells. The results suggest that antigen-specific proliferative memory T cells, which may be Th1-like memory cells, preferentially migrate to peripheral lymph nodes independent of their site of induction.     

Generation of intestinal mucosal lymphocytes in SCID mice reconstituted with mature, thymus-derived T cells

Transfer of peripheral lymph node lymphocytes to SCID mice leads to the long term establishment of mucosal T lymphocytes within the epithelium and lamina propria of the small and large intestines. Analysis of engrafted intraepithelial lymphocytes (IEL) showed that they had acquired a surface phenotype that in several respects is typical of IEL. In addition, the functional profile of engrafted IEL derived from lymph node T cells was similar to that of normal IEL; as the donor-derived T cells exhibited a strong cytolytic activity, a poor proliferative response to mitogenic stimuli, and a tendency to home and expand specifically in the intestine upon transfer to secondary SCID recipients. Optimal engraftment of intestinal T cells required bacterial flora, as the number of lymphocytes was greatly reduced in SCID recipients with a reduced flora. These results demonstrate that mature, thymus-derived T cells can migrate to the intestine and become functionally specialized to the intestinal milieu. The acquisition of phenotypic markers characteristic of the intestinal microenvironment by engrafted cells suggests that T cell migration of lymphocytes to the SCID intestine is not aberrant, but it may reflect processes that are ongoing in immunocompetent mice. Furthermore, these data suggest that the homing and/or expansion of typical, thymus-derived T cells in the intestine may be driven by luminal Ags such as those derived from bacterial flora.     

Preparation of recombinant gilthead seabream (Sparus aurata) growth hormone and its use for stimulation of larvae growth by oral administration

Optimal protective immunity against babesial infection is postulated to require both complement-fixing and opsonizing antibodies in addition to gamma interferon (IFN-gamma)-mediated macrophage activation. The rhoptry-associated protein 1 (RAP-1) of Babesia bigemina induces partial protective immunity and is a candidate vaccine antigen. Previous studies demonstrated that cattle immunized with native protein that were subsequently protected against challenge had a strong IFN-gamma and weaker interleukin-4 (IL-4) response in immune lymph node lymphocytes that reflected the cytokine profile of the majority of CD4(+) T-cell clones obtained from peripheral blood. RAP-1-specific T helper (Th) cell clones that coexpress IFN-gamma and IL-4 are typical of numerous parasite-specific clones examined. However, the function of such cells as helper cells to enhance immunoglobulin secretion by bovine B cells has not been reported. In cattle, both immunoglobulin G1 (IgG1) and IgG2 can fix complement, but IgG2 is the superior opsonizing subclass. Therefore, studies were undertaken to ascertain the functional relevance of RAP-1-specific, CD4(+) Th0 cells as helper cells to enhance IgG1 and/or IgG2 production by autologous B lymphocytes. For comparison, Th0 clones specific for the metazoan parasite Fasciola hepatica that expressed relatively more IL-4 than the B. bigemina-specific Th cells were similarly assayed. B. bigemina RAP-1-specific clones could enhance production of both IgG1 and IgG2 by autologous B cells, whereas Th cell clones specific for F. hepatica enhanced predominantly IgG1 production. The capacity to enhance IgG2 production was associated with production of IFN-gamma by Th cells cocultured with B cells, antigen, and IL-2. The in vitro helper T-cell activity of these T-cell clones was representative of the in vivo serologic responses, which were composed of a mixed IgG1-IgG2 response in B. bigemina RAP-1 immune cattle and a biased IgG1 response in F. hepatica-immune cattle.     

The role of in vitro-induced lymphocyte apoptosis in feline immunodeficiency virus infection: correlation with different markers of disease progression

Human immunodeficiency virus infection is characterized by a progressive decline in the number of peripheral blood CD4(+) T lymphocytes, which finally leads to AIDS. This T-cell decline correlates with the degree of in vitro-induced lymphocyte apoptosis. However, such a correlation has not yet been described in feline AIDS, caused by feline immunodeficiency virus (FIV) infection. We therefore investigated the intensity of in vitro-induced apoptosis in peripheral blood lymphocytes from cats experimentally infected with a Swiss isolate of FIV for 1 year and for 6 years and from a number of long-term FIV-infected cats which were coinfected with feline leukemia virus. Purified peripheral blood lymphocytes were either cultured overnight under nonstimulating conditions or stimulated with phytohemagglutinin and interleukin-2 for 60 h. Under stimulating conditions, the isolates from the infected cats showed significantly higher relative counts of apoptotic cells than did those from noninfected controls (1-year-infected cats, P = 0.01; 6-year-infected cats, P = 0.006). The frequency of in vitro-induced apoptosis was inversely correlated with the CD4(+) cell count (P = 0. 002), bright CD8(+) cell count (P = 0.009), and CD4/CD8 ratio (P = 0. 01) and directly correlated with the percentage of bright major histocompatibility complex class II-positive peripheral blood lymphocytes (P = 0.004). However, we found no correlation between in vitro-induced apoptosis and the viral load in serum samples. Coinfection with feline leukemia virus enhanced the degree of in vitro-induced apoptosis compared with that in FIV monoinfected cats. We concluded that the degree of in vitro-induced apoptosis was closely related to FIV-mediated T-cell depletion and lymphocyte activation and could be used as an additional marker for disease progression in FIV infection.     

Mechanisms associated with defective TH1 cytokine production in HIV infection

Qualitative and quantitative changes in immune functions of different T-cell subsets associated with infection by human immunodeficiency virus type 1 (HIV-1) were analyzed by flow cytometric assessment of intracytoplasmic cytokines. The T(H)1 cytokines, interleukin-2 (IL-2) and interferon-gamma (IFN-gamma), were produced by both CD4 and CD8 T-cell subsets. When normal peripheral blood mononuclear cells (PBMC) were activated in culture, both cytokines were produced predominantly by CD4 (CD4) cell and only a minor fraction of normal CD8 cells produced these cytokines. In the cultures of PBMC from HIV-1-infected individuals (HIV+PBMC), more HIV+CD8 cells produced IL-2 and IFN-gamma. Production of IFN-gamma by HIV+CD4 cells was markedly reduced, while IL-2nd tumor necrosis factor-alpha (TNF-alpha) production by HIV+CD4 remained relatively intact until the disease progressed further. Normal CD4 cells which were isolated by using a cell sorter, FACSCalibur was still able to produce IL-2 and TNF-alpha. But for full production of IFN-gamma, normal CD4 required some accessory cells, the identity of which could not yet be established.     

Recombinant modified vaccinia virus Ankara-simian immunodeficiency virus gag pol elicits cytotoxic T lymphocytes in rhesus monkeys detected by a major histocompatibility complex class I/peptide tetramer

The utility of modified vaccinia virus Ankara (MVA) as a vector for eliciting AIDS virus-specific cytotoxic T lymphocytes (CTL) was explored in the simian immunodeficiency virus (SIV)/rhesus monkey model. After two intramuscular immunizations with recombinant MVA-SIVSM gag pol, the monkeys developed a Gag epitope-specific CTL response readily detected in peripheral blood lymphocytes by using a functional killing assay. Moreover, those immunizations also elicited a population of CD8+ T lymphocytes in the peripheral blood that bound a specific major histocompatibility complex class I/peptide tetramer. These Gag epitope-specific CD8+ T lymphocytes also were demonstrated by using both functional and tetramer-binding assays in lymph nodes of the immunized monkeys. These observations suggest that MVA may prove a useful vector for an HIV-1 vaccine. They also suggest that tetramer staining may be a useful technology for monitoring CTL generation in vaccine trials in nonhuman primates and in humans.     

The relationship of blood lymphocytes to the recirculating lymphocyte pool

Lymphocyte recirculation facilitates the detection and elimination of pathogens and the dissemination of immunologic memory. It is generally assumed that all small lymphocytes in the blood are actively recirculating, yet there is little quantitative data directly comparing the migration of this population with actively recirculating, lymph-derived lymphocytes. In this study blood lymphocytes were labeled with fluorescein isothiocyanate (FITC), and lymph lymphocytes were labeled with CM-DiI, reinfused intravenously, and monitored in blood and lymph. After equilibration the concentration of blood lymphocytes was several times higher in blood than in lymph, whereas lymph lymphocytes displayed the opposite behavior. This suggested that blood lymphocytes did not recirculate as efficiently as lymph lymphocytes, so we examined the following blood lymphocyte subsets in greater detail: B cells, CD4+, CD8+, and gammadelta T cells. Within 4 hours postinjection the percentage of FITC+ CD8+ and CD4+ lymphocytes fell in the blood and remained significantly lower than the injected sample. In contrast, the concentration of FITC+ gammadelta T cells did not change, and the percentage of FITC+ B cells increased. These data suggest that subpopulations of B and perhaps gammadelta T lymphocytes in the blood do not recirculate efficiently through lymph nodes.     

A mucosal intranet: intestinal epithelial cells down-regulate intraepithelial, but not peripheral, T lymphocytes

Epithelial cells and lymphocytes, including gammadelta and alphabeta T cells, in the gastrointestinal tract epithelium represent a major host defense intranet that is incompletely understood. Cell-to-cell interactions between intraepithelial lymphocytes (IELs) and intestinal epithelial cells (IECs) comprise this intranet, and we have assessed the role of IECs in the regulation of gammadelta and alphabeta T cell responses. When highly purified CD3+ IEL T cells were stimulated via the TCR-CD3 complex, high proliferative responses and cytokine synthesis were induced. However, the addition of viable IECs or purified IEC membranes (mIEC) down-regulated T cell proliferative and cytokine responses. Further, the inhibitory effect of mIEC was not restored by antibodies to TGF-beta, CD1d, E-cadherin, or MHC class I or II. This inhibitory effect was noted for both gammadelta and alphabeta T cell subsets from IELs, and mRNA levels were reduced for both Th1 (IL-2 and IFN-gamma) and Th2 (IL-4 and IL-5) cytokines in gammadelta and alphabeta IELs. In contrast, a purified membrane fraction obtained from thymocytes did not inhibit IEL proliferative responses. Further, mIEC did not inhibit splenic alphabeta T cell proliferative responses. These findings show that cell-to-cell interactions between intraepithelial gammadelta and alphabeta T cells and IECs occur via cell surface molecules, suggesting an intranet to prevent potential inflammatory responses at the intestinal mucosal surface.     

Lake Vera revisited: parity and survival rates of Anopheles punctipennis at the site of a malaria outbreak in the Sierra Nevada foothills of California

FTY720, a novel immunosuppressant, sequesters circulating mature lymphocytes, especially T cells, within lymph nodes and Peyer's patches by accelerating lymphocyte homing, and thereby causes lymphocyte depletion in the blood. The FTY720-induced acceleration of lymphocyte homing appears to be mediated by lymphocyte homing receptors including CD62L, CD49d/beta7, and CD11a/CD18. In this study, expressions of CD62L, CD49d and CD11a on T cells in the peripheral blood, lymph nodes and Peyer's patches were analysed by flow cytometry in rats given FTY720 (1 mg/kg) orally. FTY720 markedly decreased the number of peripheral blood T cells, while not affecting CD62L, CD49d and CD11a expressions at 1-3 hr after administration. In contrast, both the frequency of CD62L-positive T cells and intensity of CD62L expression on T cells were increased in Peyer's patches but not lymph nodes at 3 hr after administration of FTY720. CD49d and CD11a expressions on T cells were unaffected by FTY720 in both Peyer's patches and lymph nodes at the same point in time. On the other hand, analysis of lymphocyte homing with calcein-labelled lymphocytes and anti-CD62L monoclonal antibody (mAb) confirmed that FTY720 predominantly increased CD62L-dependent lymphocyte homing to Peyer's patches. These findings indicate that FTY720 increases the frequency of CD62L-positive T cells by accelerating CD62L-predominant homing in Peyer's patches.     

Gut-derived intraepithelial lymphocytes induce long term immunity against Toxoplasma gondii

Intraepithelial lymphocytes (IEL) of the intestine represent an important barrier in the prevention of infection against orally acquired pathogens. Adoptive transfer of Ag-primed IEL into a naive host can protect against challenge. Using a murine model, we demonstrate in two genetically distinct mouse strains (C57BL/6 and CBA/J) that protective IEL can be isolated at specific times after oral infection with cysts containing bradyzoites. Adoptive transfer of IEL obtained from the intestine of infected mice at these specific times can provide long term protection, as determined by mortality and cyst number against challenge. The protective IEL appear to be CD8+, TCR-alpha/beta and are at least partially dependent upon the presence of TCR-gamma/delta T cells in the host. Endogenous production of the pivotal cytokine, IFN-gamma, is essential for host immunity. These findings demonstrate that gut-derived IEL represent a potentially important mechanism to provide long term immunity to the host.