Production of colony-stimulating factors during pneumonia caused by Chlamydia trachomatis

T lymphocyte immunity in host defence against Chlamydia trachomatis and its implication for vaccine development

Chlamydia trachomatis is an obligate intracellular bacterial pathogen that causes several significant human infectious diseases, including trachoma, urethritis, cervicitis and salpingitis, and is an important cofactor for transmission of human immunodeficiency virus. Until very recently, over three decades of research effort aimed at developing a C trachomatis vaccine had failed, due mainly to the lack of a precise understanding of the mechanisms for protective immunity. Although most studies concerning protective immunity to C trachomatis have focused on humoral immune responses, recent studies have clearly shown that T helper-1 (Th1)-like CD4 T cell-mediated immune responses play the dominant role in protective immunity. These studies suggest a paradigm for chlamydial immunity and pathology based on the concept of heterogeneity (Th1/Th2) in CD4 T cell immune responses. This concept for chlamydial immunity offers a rational template on which to base renewed efforts for development of a chlamydial vaccine that targets the induction of cell-mediated Th1 immune responses.

Regulation of hematopoiesis in vitro and in vivo by invariant NKT cells

Invariant natural killer T cells (iNKT cells) are a small subset of immunoregulatory T cells highly conserved in humans and mice. On activation by glycolipids presented by the MHC-like molecule CD1d, iNKT cells promptly secrete T helper 1 and 2 (Th1/2) cytokines but also cytokines with hematopoietic potential such as GM-CSF. Here, we show that the myeloid clonogenic potential of human hematopoietic progenitors is increased in the presence of glycolipid-activated, GM-CSF–secreting NKT cells; conversely, short- and long-term progenitor activity is decreased in the absence of NKT cells, implying regulation of hematopoiesis in both the presence and the absence of immune activation. In accordance with these findings, iNKT-cell–deficient mice display impaired hematopoiesis characterized by peripheral-blood cytopenias, reduced marrow cellularity, lower frequency of hematopoietic stem cells (HSCs), and reduced early and late hematopoietic progenitors. We also show that CD1d is expressed on human HSCs. CD1d-expressing HSCs display short- and long-term clonogenic potential and can present the glycolipid α-galactosylceramide to iNKT cells. Thus, iNKT cells emerge as the first subset of regulatory T cells that are required for effective hematopoiesis in both steady-state conditions and under conditions of immune activation.

Linking immunity and hematopoiesis by bone marrow T cell activity

Two different levels of control for bone marrow hematopoiesis are believed to exist. On the one hand, normal blood cell distribution is believed to be maintained in healthy subjects by an "innate" hematopoietic activity, i.e., a basal intrinsic bone marrow activity. On the other hand, an "adaptive" hematopoietic state develops in response to stress-induced stimulation. This adaptive hematopoiesis targets specific lineage amplification depending on the nature of the stimuli. Unexpectedly, recent data have shown that what we call "normal hematopoiesis" is a stress-induced state maintained by activated bone marrow CD4+ T cells. This T cell population includes a large number of recently stimulated cells in normal mice whose priming requires the presence of the cognate antigens. In the absence of CD4+ T cells or their cognate antigens, hematopoiesis is maintained at low levels. In this review, we summarize current knowledge on T cell biology, which could explain how CD4+ T cells can help hematopoiesis, how they are primed in mice that were not intentionally immunized, and what maintains them activated in the bone marrow.

Mouse strain-dependent variation in the course and outcome of chlamydial genital tract infection is associated with differences in host response

Whether there is a pathogenic or protective outcome to chlamydial infection may be defined by the host response. We infected C57BL/6 (C57) and C3H/HeN (C3H) mice with the human biovar of Chlamydia trachomatis, serovar E, and, in select experiments, with the mouse pneumonitis agent of C. trachomatis (MoPn). We compared the courses of infection, histopathology, and host responses that resulted from these infections. The duration of infection with either chlamydial biovar was significantly increased in the C3H strain of mice. The intensity of infection was examined in mice infected with serovar E, and it was significantly increased in the C3H strain. Histopathology revealed the incidence of severe hydrosalpinx to be significantly greater in C3H mice than in C57 mice. In contrast, severe distention of the uterine horns was observed in all infected C57 mice compared to none of the C3H mice infected with serovar E and only 25% of those infected with MoPn. Acute inflammation was significantly increased in the uterine horns of C57 mice compared to that of C3H mice. Examination of antigen-specific responses revealed qualitatively similar responses in the two strains. Determination of gamma interferon- versus interleukin 4- producing cells revealed the predominance of a Th1 response in both strains. Serum enzyme-linked immunosorbent assays for immunoglobulin G1 (IgG1) and IgG2a revealed a predominance of IgG2a antibody in both strains, although the levels of antibody were significantly greater in C3H mice. Lymphocyte proliferation studies revealed increased proliferation in the iliac nodes of both strains at 1 to 3 weeks after infection. Because of the early eradication of infection observed in the C57 strain, we explored the relative production of tumor necrosis factor alpha (TNF-alpha) in the two strains. TNF-alpha levels were significantly increased in the genital tract secretions of C57 mice compared to that of C3H mice during the first week of infection. Increased TNF-alpha may be beneficial to the host by leading to earlier eradication of infection, thereby preventing infection of the oviduct and thus the major disease sequelae associated with chlamydial infection of the genital tract.

Humoral and cellular immunity in secondary infection due to murine Chlamydia trachomatis

A murine model of pneumonia due to the mouse pneumonitis agent (MoPn [murine Chlamydia trachomatis]) in mice deficient in CD4+ T-cell function (major histocompatibility complex [MHC] class II function [class II-/-], CD8+ T-cell function (beta2-microglobulin deficient, MHC class I deficient [Beta2m-/-]), B-cell function (C57BL/10J-Igh(tm1Cgn) [Igh-/-]), and gamma interferon (IFN-gamma) (C57BL/6-Ifg(tm1) [Ifg-/-]) or interleukin-4 (C57BL/6J(tm1Cgn29) [IL4-/-]) production was employed to determine if each of these mechanisms was critical to resistance against reinfection by C. trachomatis or if alternate compensatory mechanisms existed in their absence which could potentially be exploited in vaccine development. Resistance to reinfection with MoPn was heavily dependent on CD4+ T cells. CD4 T-cell-deficient MHC class II-/- mice were very susceptible to reinfection with MoPn, showing the critical importance of this cell to resistance. These mice lacked antibody production but did produce IFN-gamma, apparently by mechanisms involving NK and CD8+ T cells. Neutralization of IFN-gamma in these mice led to a borderline increase in susceptibility, showing a possible role (albeit small) of this cytokine in this setting. Tumor necrosis factor alpha (TNF-alpha) was also present at increased levels in these mice. Igh-/- B-cell-deficient mice which produce no antibody to MoPn were only modestly more susceptible to reinfection than immunized B-cell-intact controls, showing that antibody, including lung immunoglobulin A, is not an absolute requirement for relatively successful host defense in this setting. Levels of lung IFN-gamma and TNF-alpha were elevated in Igh-/- mice compared to those in controls. IL-4-/- mice (deficient in Th2 function) could develop normal resistance to reinfection with MoPn. Conversely, normal mice rendered partially IFN-gamma deficient by antibody depletion were somewhat impaired in their ability to develop acquired immunity to MoPn, again indicating a role for this cytokine in host defense against rechallenge. Of most importance, however, congenitally IFN-gamma-deficient Ifg-/- mice (which have elevated levels of other cytokines, including TNF-alpha and granulocyte-macrophage colony-stimulating factor) are paradoxically more resistant to MoPn rechallenge than controls, showing that IFN-gamma is not an absolute requirement for acquired resistance and implying the presence of very effective compensatory host defense mechanism(s). In vivo depletion of TNF-alpha significantly increased MoPn levels in the lungs in these mice. Thus, resistance to reinfection in this model is flexible and multifactorial and is heavily dependent on CD4+ T cells, with a probable role for IFN-gamma and TNF-alpha and a possible modest role for Th1-dependent antibody. Since IFN-gamma was dispensable in host defense, the highly effective mechanism or mechanisms which can compensate for its absence (which include TNF-alpha) deserve further study.

Chlamydia trachomatis growth stimulates interleukin 8 production by human monocytic U-937 cells

Growth of Chlamydia trachomatis serotypes L2 and L3 in a human monocytic cell line, U-937, increased the rate of interleukin 8 (IL-8) release 100-fold. Heat-killed chlamydiae induced a 10-fold-lower level of production of IL-8. IL-8 may play an important role in the inflammatory reaction to chlamydial infection.

Role of CD8 T cells in primary Chlamydia infection

The role of CD4 and CD8 T cells in primary Chlamydia trachomatis pneumonia was investigated by using in vivo depletion techniques to eliminate T-cell populations. Reduction of either CD4 T cells or CD8 T cells caused a significant increase in organism burden in the lungs, as measured by both quantitative culture and detection of chlamydial antigen on day 14 postinfection. Chlamydia-specific antibody levels in plasma or antigen-induced gamma interferon (IFN-gamma) production by spleen cells was dramatically reduced by depletion of CD4 cells. The reduction in IFN-gamma achieved by depletion of CD8 cells did not reach statistical significance. In the survival studies, depletion of CD4 cells led to a significant increase in mortality. Although there was a trend toward higher mortality, depletion of CD8 cells did not significantly increase mortality. The role of CD8 T cells in host defense was clarified in studies using beta 2-microglobulin-deficient (major histocompatibility class I antigen-deficient, C1D) mice which are defective in CD8 T-cell function. In this model, a significant increase in organism burden was seen during infection in C1D mice compared with that C57BL/6 controls and a significant increase in mortality was observed as well. However, surviving C1D mice were able to clear the infection by day 34. C1D mice had increased numbers of CD4 T cells in both the spleen and the lungs during infection compared with those of C57BL/6 controls. IFN-gamma in C57BL/6 mice was produced by both CD4 and CD8 cells. Thus, there is a protective role for both CD4 and CD8 cells in host defense against Chlamydia infection, but the former appear to be dominant.

Gamma interferon levels during Chlamydia trachomatis pneumonia in mice

Host defense against murine Chlamydia trachomatis (mouse pneumonitis agent [MoPn]) in a murine model was investigated. Gamma interferon (IFN-gamma) was produced in the lungs by both MoPn-susceptible nude athymic (nu/nu) and MoPn-resistant heterozygous (nu/+) mice. In vivo depletion of IFN-gamma in nu/nu mice led to exacerbation of infection. Fluorescence-activated cell sorter analysis disclosed induction of GL3 antibody-positive cells (putatively gamma/delta+ T cells) in nu/nu mouse lung during infection with MoPn. Treatment of nu/nu mice in vivo with antibody to NK cells (anti-asialo GM1 antibody) or to gamma/delta cells (UC7-13D5) did not significantly decrease IFN-gamma production in the lung. However, treatment of severe combined immunodeficiency mice (which lack gamma/delta cells) with antibody to NK cells significantly reduced lung IFN-gamma levels.

Both immunity and hyperresponsiveness to Pneumocystis carinii result from transfer of CD4+ but not CD8+ T cells into severe combined immunodeficiency mice

The opportunistic pathogen Pneumocystis carinii (Pc) is considered to be the leading cause of morbidity in patients with AIDS. It is important, therefore, to determine the immunological mechanisms of resistance to Pc. We have taken advantage of the lack of both T and B lymphocytes in severe combined immunodeficiency (scid) mice to determine the critical factors in resistance to spontaneously acquired Pc pneumonia. Using adoptive transfer of unfractionated or fractionated lymphocyte subsets or hyperimmune serum from congenic normal donors, we have demonstrated that effective immunity to Pc results from the action of CD4+ but not CD8+ T cells (in the absence of antibody) or from humoral immunity (in the absence of T cells). However, responses of CD4+ T cells (but not antibody) to already well-established burdens of Pc are often accompanied by a fatal hyperinflammatory reaction. The activity of CD4+ T cells against Pc thus illustrates a broadly applicable principle that T cell immunity represents a critical balance between consequences beneficial and harmful to the host.

Comparative evaluation of the colony-stimulating factors induction potential of Plasmodium cynomolgi-infected monkey erythrocytes and soluble antigens

Plasmodium cynomolgi total antigens soluble in culture medium (P.c.SA), and noninfective P. cynomolgi-infected monkey erythrocytes (P.c.IE) were compared for their potential to induce colony-stimulating factors (CSFs). When injected intravenously in monkeys, both preparations induced an increase in the serum CSFs levels; P.c.IE appeared to be 1.6-fold more potent than the P.c.SA. In vitro P.c.IE induced 1.8-fold more CSF by monkey blood monocyte-derived macrophages than P.c. However, both in vivo and in vitro, the peak CSFs levels induced by P.c.SA were attained apparently 8 h earlier. CSF generated by P.c.SA and P.c.IE induced the formation of macrophage, granulocyte and granulocyte-macrophage colonies, in vitro; P.c.IE-generated CSF induced the formation of significantly (P < 0.01) higher numbers of granulocyte-macrophage colonies, indicating that the CSF induced by them stimulated different biological responses. The CSF induction appeared to be LPS-independent.