Central Tolerance of T Cells

The immune system is constructed to tolerate self antigens but give vigorous responses to foreign antigens. How this state of self/nonself discrimination is maintained is controversial. In the case of T cells, many self antigens are transported to the thymus via the bloodstream and induce tolerance (clonal deletion) of self-reactive thymocytes in situ. Although such central tolerance in the thymus is well documented, it is often argued that full induction of tolerance requires peripheral mechanisms such as suppression or induction of anergy. This article proposes that steady-state tolerance of T cells to self components is due solely to central tolerance to circulating self antigens combined with sequestration of tissue-specific antigens. Backup mechanisms for tolerance do exist but such immunoregulation only operates when self tolerance breaks. This scheme allows the immune system to give unrestricted primary responses to foreign antigens.     

Function of Helper T Cells in the Memory CTL-mediated Anti-tumor Immunity

CD4 Tcellsarerequiredforthegenerationandmainte nanceofcytolyticCD8 Tcellsandareessentialforthe generationofbothcellularandhumoralimmuneresponses. However,thecontributionofCD4 Tcellstothemainte nanceofanti tumorimmunityisstillthesubjectofintense investig…     

Coelomocytes as Effector Cells in Eartworm Immunity

The results from this study support the following hypothetical mechanism for the rejection of xenografts by Lumbricus. Initially, coelomocytes are attracted to xenografts due to the stimulus of tissue injury. This results in clumping or nodule formation around injured and loose muscle fibers, and a general clumping of baso-phils. Clumping may entran acidophilic cells and/or attract such cells to the graft site. Because the graft is a foreign tissue, its foreignness also stimulates a cellular response. Basophils invade the muscular structure of the xenograft and more acidophilic cells accumulate at the graft site. The acidophilic cells have the canacity to digest the connective tissue elements which hold the muscle fibers of the graft in place. Dissolution of these connective tissue elements results in the release of muscle fibers. The presence of free foreign muscular tissue in the coelomic cavity acts as a stimulus for further accumulations of basophilic cells, which in turn form more capsules and may attract more acidophils. Thus there is a continuous erosion of xenograft muscle by acidophils and a clearing away of debris by basophils. This process eventually leads to the complete destruction of a xenograft.

Autografts stimulate the accumulation of basophils due to the presence of injured tissue. The presence of cell clumps and/or injured tissue also causes acidophilic cells to accumulate under the graft. Only injured or dead tissue is acted upon by the coelomic cells since the stimulation of any further cellular invasion into the graft by a foreign antigen, is not present in autografts. Acidophilic coelomic cells, either do not release substances that can attack the connective tissues of autografts, or the substances released by these cells does not react with non-injured self tissue. This mechanism together with other information concerning specificity and anamnesis in the rejection response of the annelid Lumbricus terrestris, offers further support for a true immunologi-cal response to tissue grafts in an invertebrate.     

Coelomocytes as Effector Cells in Eartworm Immunity

The results from this study support the following hypothetical mechanism for the rejection of xenografts by Lumbricus. Initially, coelomocytes are attracted to xenografts due to the stimulus of tissue injury. This results in clumping or nodule formation around injured and loose muscle fibers, and a general clumping of baso-phils. Clumping may entran acidophilic cells and/or attract such cells to the graft site. Because the graft is a foreign tissue, its foreignness also stimulates a cellular response. Basophils invade the muscular structure of the xenograft and more acidophilic cells accumulate at the graft site. The acidophilic cells have the canacity to digest the connective tissue elements which hold the muscle fibers of the graft in place. Dissolution of these connective tissue elements results in the release of muscle fibers. The presence of free foreign muscular tissue in the coelomic cavity acts as a stimulus for further accumulations of basophilic cells, which in turn form more capsules and may attract more acidophils. Thus there is a continuous erosion of xenograft muscle by acidophils and a clearing away of debris by basophils. This process eventually leads to the complete destruction of a xenograft.

Autografts stimulate the accumulation of basophils due to the presence of injured tissue. The presence of cell clumps and/or injured tissue also causes acidophilic cells to accumulate under the graft. Only injured or dead tissue is acted upon by the coelomic cells since the stimulation of any further cellular invasion into the graft by a foreign antigen, is not present in autografts. Acidophilic coelomic cells, either do not release substances that can attack the connective tissues of autografts, or the substances released by these cells does not react with non-injured self tissue. This mechanism together with other information concerning specificity and anamnesis in the rejection response of the annelid Lumbricus terrestris, offers further support for a true immunologi-cal response to tissue grafts in an invertebrate.     

Heterogenous Populations of Tissue-Resident CD8+ T Cells Are Generated in Response to Infection and Malignancy

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CD4+ T Cells and Antibody Are Required for Optimal Major Outer Membrane Protein Vaccine-Induced Immunity to Chlamydia muridarum Genital Infection

Despite effective antimicrobial chemotherapy, control of Chlamydia trachomatis urogenital infection will likely require a vaccine. We have assessed the protective effect of an outer membrane protein-based vaccine by using a murine model of chlamydial genital infection. Female mice were first vaccinated with Chlamydia muridarum major outer membrane protein (MOMP) plus the adjuvants CpG-1826 and Montanide ISA 720; then they were challenged with C. muridarum. Vaccinated mice shed 2 log₁₀ to 3 log₁₀ fewer inclusion-forming units (IFU) than ovalbumin-vaccinated or naïve animals, resolved infection sooner, and had a lower incidence of hydrosalpinx. To determine the relative contribution of T cells to vaccine-induced protection, mice were vaccinated, depleted of CD4⁺ or CD8⁺ T cells, and then challenged vaginally with C. muridarum. Depletion of CD4⁺ T cells, but not depletion of CD8⁺ T cells, diminished vaccine-induced protection, with CD4-depleted mice shedding 2 log₁₀ to 4 log₁₀ more IFU than CD8-depleted or nondepleted mice. The contribution of antibodies to vaccine-induced protection was demonstrated by the absence of protective immunity in vaccinated B-cell-deficient mice and by a 2 log₁₀ to 3 log₁₀ decrease in bacterial shedding by mice passively administered an anti-MOMP serum. Thus, optimal protective immunity in this model of vaccine-induced protection depends on contributions from both CD4⁺ T cells and antibody.New cases of sexually transmitted diseases number more than 340 million worldwide annually and pose a formidable health risk to infected individuals (67-69). It is estimated that Chlamydia trachomatis, the causative agent of chlamydia, is responsible for more than 92 million of these cases. In the United States, where C. trachomatis infections are the infections most commonly reported to the Centers for Disease Control and Prevention, there are more than 4 million new cases each year (14, 67). As a bacterial agent of infection, C. trachomatis can be eradicated efficiently with appropriate antibiotic treatment, but more than 50% of infected individuals are asymptomatic and therefore lack the impetus to seek treatment (14). When left untreated, infection in women can lead to pelvic inflammatory disease, ectopic pregnancy, and tubal factor infertility and can cause severe and sometimes irreparable damage to the reproductive organs (14, 67). To combat the high rate of infection and disease, the development of an efficacious vaccine is critical.Trachoma vaccine trials using whole organisms in the 1950s and 1960s had mixed results, with some studies inducing only partial, serovar-specific, short-lived immunity (4). In one study, a subset of vaccine trial participants experienced an increased incidence of disease and exacerbated pathology relative to that of their unvaccinated counterparts upon reexposure to chlamydiae, which led many researchers to abandon the use of whole organisms in immunizations (7, 8). Since then, no other human vaccine trials targeting ocular or urogenital C. trachomatis infections have been published. Instead, researchers have focused their efforts on animal models of ocular and genital infection.To this end, the murine model of chlamydial genital infection, which closely mimics acute genital infection in women, has been employed extensively for the study of the immunological parameters of infection and for vaccine development. Mice infected with C. muridarum naturally resolve infection in approximately 4 weeks and develop long-lived adaptive immunity that markedly protects against reinfection (3, 37). Infection elicits Chlamydia-specific CD4⁺ T cells, CD8⁺ T cells, and antibody, but only CD4⁺ T cells are necessary for resolution of the primary infection (42). In contrast, immunity to reinfection is dominated by both protective CD4⁺ T cells and antibody (38). Clearance and immunity are highly dependent on a Th1-type response, specifically gamma interferon (IFN-γ)-secreting CD4 cells (9). On the other hand, Th2 responses are associated with scarring and immunopathology (62). For example, antibody responses dominated by IgG1 are not protective and may be associated with an increase in pathology, whereas anti-chlamydial antibodies of the IgG2a and IgG2b isotypes are associated with a protective response (51).Using knowledge of the protective response gleaned from the murine model of infection-induced immunity, investigators have made modest strides toward the development of an efficacious vaccine. Studies utilizing whole elementary body (EB) immunization have induced significant protection, though most of these studies have limited real-world application. One notable example that induced almost sterilizing immunity involved the passive transfer of dendritic cells pulsed ex vivo with nonviable chlamydiae (65). Subunit antigen vaccines represent the bulk of vaccine studies, and vaccines based on combinations of a number of chlamydial antigens, adjuvants, and delivery systems have had various degrees of success in preventing infection (8, 22, 62). Chlamydial antigens, including secreted proteins, such as chlamydial protease-like activity factor (CPAF) (16, 33, 43-46), and membrane associated proteins, such as PorB (26, 30) and IncA (33), have also been used in subunit vaccines; however, the vast majority of studies have focused on the major outer membrane protein (MOMP), an immunodominant antigen in both human and animal studies (22, 62). Novel delivery systems, including Vibrio cholerae ghosts and cationic liposomes, have been introduced into chlamydial vaccine research, and while initial studies have shown incomplete protection, these systems may have the potential to elicit protective responses against chlamydial genital infection when used in conjunction with appropriate antigens (2, 19, 20, 23).Despite substantial effort, no vaccine licensed for human use is currently available. Recently, a MOMP-based vaccine utilizing the adjuvants CpG-1826 and Montanide ISA 720, which together drive a strong Th1-type response, has been shown to confer considerable protection when mice are challenged directly in the upper genital tract with C. muridarum (51). In our current study, we sought to determine if this vaccine protected against vaginal challenge (the natural route of infection) and to evaluate the contributions of T cells and antibody to the vaccine-induced protective response. We found that the MOMP vaccine conferred significant protection against vaginal challenge and protected against infection-induced pathology (hydrosalpinx). Furthermore, optimal protection was dependent on both CD4⁺ T cells and antibody.     

Immunity in Experimental Murine Filariasis: Roles of T and B Cells Revisited

We have reevaluated the contributions of T and B cells in Brugia malayi infection by utilizing knockout mice on a uniform background (C57BL/6J). We find that B-cell-deficient mice are more permissive to infection than T-cell-deficient mice.     

The Plasticity of γδT Cells: Innate Immunity, Antigen Presentation and New Immunotherapy

Several signals influence dendritic cell (DC) functions and consequent the immune responses to infectious pathogens. Our recent findings provide a new model of intervention on DCs implicating human γδ T cell stimuli. Vγ9Vδ2 T cells represent the major subset of circulating human γδ T cells and can be activated by non-peptidic molecules derived from different microorganisms or abnormal metabolic routes. With activated-Vγ9Vδ2 T cell co-culture, immature DCs acquire features of mature DCs, such as increasing the migratory activity, up-regulating the chemokine receptors, and triggering the Thl immune response. Similar to the NK-derived signals, DC activation is mediated by soluble factors as well as cell-to-cell contact. Many non-peptidic molecules including nitrogen- containing bisphosphonates and pyrophosphomonoester drugs, can stimulate the activity of Vγ9Vδ2 T cells in vitro and in vivo. The relatively low in vivo toxicity of many of these drugs makes possible novel vaccine and immune-based strategies against infectious diseases. Cellular & Molecular Immunology. 2008;5(3):161-170.     

Transfer of Immunity Against Listeria monocytogenes by T Cells Purified by a Positive Selection Technique

Affinity columns prepared with rabbit antibody to the F(ab')(2) fragment of rat immunoglobulin were used to separate rat thoracic duct lymphocytes into sub-populations that differ with respect to the density of their surface membrane immunoglobulin. Using this technique, it was shown that lymphocytes in the DNA synthetic (S) phase of the mitotic cycle are added in increased number to the lymph of rats infected with Listeria monocytogenes. The great majority of these S-phase cells lacked a high density of surface immunoglobulin as indicated by their failure to bind to the immunoabsorbent. Cells which can protect recipient rats against a challenge infection with L. monocytogenes also segregated with nonadherent thoracic duct lymphocytes obtained from Listeria-immune donors. These protective cells realized their full immunological potential only in recipients that shared histocompatibility-gene-coded structures with the immune lymphocyte donors. The above findings accord with the view that immunity to L. monocytogenes is mediated in rats by activated T cells which are formed as part of the animal's cell-mediated response to infection. Although Listeria-protective lymphocytes concentrate in the nonadherent, T-cell-enriched fraction, it was consistently observed that the adherent, B-cell-enriched fractions of immune donor thoracic duct lymphocytes also could transfer a low level of antimicrobial resistance. This immunity was restricted in allogeneic recipients, a finding which implies that the protection afforded by the adherent population is related to its content of T cells. Nonadherent S-phase lymphoblasts moved in substantial numbers from the blood into peritoneal inflammatory exudates induced by L. monocytogenes. The above finding encourages the belief that recently activated T cells realize their protective function locally in centers of infection where they have secondary effects on macrophages.     

Disruption of Coronin 1 Signaling in T Cells Promotes Allograft Tolerance while Maintaining Anti-Pathogen Immunity

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Immunity to reinfection of the genital tract of marmosets with Chlamydia trachomatis.

Eleven marmosets inoculated intra-vaginally with either of 2 serotypes (D/E and H) of Chlamydia trachomatis developed a self-limited infection which persisted usually for 10-42 days. Animals re-inoculated on one or more occasions were, however, infected generally for a shorter duration, usually 3-7 days. Curtailed infections were observed after re-inoculation with either the same or a different serotype, indicating that immunity was not serotype specific but cross-protective. IgM and/or IgG chlamydial antibody, measured by micro-immunofluorescence, developed in most of the marmosets on primary infection and was not serotype specific. The antibody titres were boosted on re-infection and there was a correlation between pre-existing high antibody titres and infections of short duration. Chlamydial infection of the genital tract was accompanied by acute inflammation which persisted in about half of the immune animals for up to several weeks despite rapid clearance of the organisms. These features of the experimental infection should help to provide a greater understanding of the immunobiology and pathogenesis of chlamydial genital-tract infections of humans.     

Inflammatory Lymphocyte in Cell-Mediated Antibacterial Immunity: Factors Governing the Accumulation of Mediator T Cells in Peritoneal Exudates

The lymphocytes which mediate immunity to infection with Listeria monocytogenes in the mouse accumulated in casein-induced peritoneal exudates. They were T cells, as evidenced by their susceptibility to anti-theta serum, but some were also destroyed by anti-immunoglobulin serum. For a given number of cells, exudate cells were at least six times more efficient than spleen cells in protecting normal recipients against lethal challenge. The extent to which mediator cells accumulated in exudates was found to be governed by the level of their production in responding lymphoid tissue and by the time available for them to migrate into an exudate. An intraperitoneal injection of casein at any stage of infection resulted in a progressive accumulation of mediator cells that continued for 3 days. The accumulation was not caused by continuous entry of cells during the whole of this period, but resulted from division of a limited number of cells that entered during the first 24 h. Accumulation of mediator cells in an exudate was associated with the conversion of a population of dividing cells into a population of nondividing T cells with a relatively short life-span.     

Immunity to murine Chlamydia trachomatis genital tract reinfection involves B cells and CD4(+) T cells but not CD8(+) T cells

CD4(+) T-helper type 1 (Th1) responses are essential for the resolution of a primary Chlamydia trachomatis genital tract infection; however, elements of the immune response that function in resistance to reinfection are poorly understood. Defining the mechanisms of immune resistance to reinfection is important because the elements of protective adaptive immunity are distinguished by immunological memory and high-affinity antigen recognition, both of which are crucial to the development of efficacious vaccines. Using in vivo antibody depletion of CD4(+) and CD8(+) T cells prior to secondary intravaginal challenge, we identified lymphocyte populations that functioned in resistance to secondary chlamydial infection of the genital tract. Depletion of either CD4(+) or CD8(+) T cells in immune wild-type C57BL/6 mice had a limited effect on resistance to reinfection. However, depletion of CD4(+) T cells, but not CD8(+) T cells, in immune B-cell-deficient mice profoundly altered the course of secondary infection. CD4-depleted B-cell-deficient mice were unable to resolve a secondary infection, shed high levels of infectious chlamydiae, and did not resolve the infection until 3 to 4 weeks following the discontinuation of anti-CD4 treatment. These findings substantiated a predominant role for CD4(+) T cells in host resistance to chlamydial reinfection of the female genital tract and demonstrated that CD8(+) T cells are unnecessary for adaptive immune resistance. More importantly, however, this study establishes a previously unrecognized but very significant role for B cells in resistance to chlamydial reinfection and suggests that B cells and CD4(+) T cells may function synergistically in providing immunity in this model of chlamydial infection. Whether CD4(+) T cells and B cells function independently or dependently is unknown, but definition of those mechanisms is fundamental to understanding optimum protective immunity and to the development of highly efficacious immunotherapies against chlamydial urogenital infections.     

Shapes that Escherichia coli Cells Can Achieve,as a Paradigm for Other Bacteria

Because the sacculi of Gram-negative rod-shaped cells are so thin, it is difficult to imagine how they grow and divide and maintain a characteristic shape and size. Abnormal cell shapes can be produced, under special conditions in Escherichia coli. These findings suggest a basis for the variety of bacterial shapes in terms of the Surface Stress Theory. Some proposals are presented to understand the form and function of rods, cocci, fusiform organisms, as well as other bacteria of other shapes using the molecular biology and physiology now known for E. coli.     

Epidermal Langerhans Cells as Accessory Cells in Con A Stimulation of T Lymphocytes in the Guinea-Pig

Stimulation of guinea-pig T cells by concanavalin A (Con A) requires Ia-antigen expressing accessory cells. Such functional accessory cells were identified among the normal epidermal cells and could be fractionated and enriched by centrifugation on discontinuous Percoll density gradients. Epidermal cells collecting at a density of 1.08 g/ml were the most effective in mediating Con A-dependent T cell proliferation, induced the highest activity of T cell growth factors (TCGF) and were enriched fivefold for Ia antigen expressing cells. A monolayer immunosorbent technique yielded a 35-fold enrichment of Ia antigen expressing epidermal cells. This cell fraction induced high levels of TCGF in the culture supernatants. Since the only cells in the normal epidermis expressing Ia antigens are the Langerhans cells, we conclude that the Langerhans cells may act as accessory cells for Con A stimulation of T cells.