Suppression of the immune response by microorganisms

Modulation of transcriptional and inflammatory responses in murine macrophages by the Mycobacterium tuberculosis mammalian cell entry (Mce) 1 complex

The outcome of many infections depends on the initial interactions between agent and host. Aiming at elucidating the effect of the M. tuberculosis Mce1 protein complex on host transcriptional and immunological responses to infection with M. tuberculosis, RNA from murine macrophages at 15, 30, 60 min, 4 and 10 hrs post-infection with M. tuberculosis H37Rv or Δ-mce1 H37Rv was analyzed by whole-genome microarrays and RT-QPCR. Immunological responses were measured using a 23-plex cytokine assay. Compared to uninfected controls, 524 versus 64 genes were up-regulated by 15 min post H37Rv- and Δ-mce1 H37Rv-infection, respectively. By 15 min post-H37Rv infection, a decline of 17 cytokines combined with up-regulation of Ccl24 (26.5-fold), Clec4a2 (23.2-fold) and Pparγ (10.5-fold) indicated an anti-inflammatory response initiated by IL-13. Down-regulation of Il13ra1 combined with up-regulation of Il12b (30.2-fold), suggested switch to a pro-inflammatory response by 4 hrs post H37Rv-infection. Whereas no significant change in cytokine concentration or transcription was observed during the first hour post Δ-mce1 H37Rv-infection, a significant decline of IL-1b, IL-9, IL-13, Eotaxin and GM-CSF combined with increased transcription of Il12b (25.1-fold) and Inb1 (17.9-fold) by 4 hrs, indicated a pro-inflammatory response. The balance between pro-and anti-inflammatory responses during the early stages of infection may have significant bearing on outcome.

Prolonged infection by Fonsecaea pedrosoi after antigenic co-stimulation at different sites in experimental murine chromoblastomycosis

In the present study, we examined prolonged infection after antigenic co-stimulation by inoculation of the fungus Fonsecaea pedrosoi at two different sites in three mouse strains (BALB/c, Swiss, and C57BL/6). Using this murine model of infection, we showed that antigen induction of infection at more than one site led to a local suppression of active lesions, which increased the time course of experimental chromoblastomycosis (CBM). Footpad infection with a simultaneous infection of the peritoneum or a mucosal site appeared to cause prolonged infection and frequent fungal disseminations. Using knockout (KO) mice, we observed that antigenic co-stimulation caused progressive illness in CD8-KO animals and an effective immune response in the absence of IL-10. In Xid mice, co-stimulation provoked chronic infection (not prolonged), suggesting that B1 B cells play an important role in the control of fungal infection. The tissue response to infection was similar in all co-stimulated mouse groups, as anatomopathologic sections revealed multifocal lesions (granuloma-like). In general, these mice had acute responses at primary antigenic sites with an intense migration of polymorphonuclear leukocytes (PMNs), whereas the distant infection sites (footpad) showed signs of chronic infection. The migration of PMNs to the secondary site (footpad) increased in the later periods of infection, especially after the disappearance of the primary antigenic focus. PMN migration was associated with lesion-dormancy breakage and fungal elimination. Our findings suggest that the host inflammatory/suppression mechanisms induced by antigenic co-stimulation to systemically fight the same pathogen act coordinately through responses that differ at the sites of infection between acute and chronic integrated healing processes that are more prolonged than an acute infection at a single site. However, the long persistence of fungal cells in the host may be linked to microbial adaptation to a parasitic infection as observed in co-stimulated Xid mice.

Interferon-gamma and interleukin-12 genes are preferentially expressed during early experimental African trypanosomiasis and suppressed by denervation of the spleen

The cross talk between the central nervous system (CNS) and the immune system includes among others, the modulation of immune responses by the autonomic nervous system. Here, we investigated the effects of a splenic denervation on cytokine induction in early experimental African trypanosomiasis. Profiles of the cytokine mRNA expression for interleukin (IL)-4, interleukin (IL)-6, interleukin (IL)-10, interleukin (IL)-12, tumour necrosis factor (TNF)-alpha, tumour necrosis factor (TNF)-beta, transforming growth factor (TGF)-beta and interferon (IFN)-gamma were examined at 4 h, 8 h and 12 h postinfection (p.i.), and in noninfected controls. Only IFN-gamma and IL-12 were significantly expressed over noninfected controls. Already at 4 h p.i. both cytokines were expressed and showed more increased levels at 12 h. Sympathetic denervation of the spleen markedly reduced the mRNA expression for both IFN-gamma and IL-12. Con A was used as a positive control and showed an enhanced mRNA expression, which was also suppressed by a splenic denervation. To demonstrate that the mRNA expression had resulted in a cytokine production, we looked for the protein level of IFN-gamma at 4 h p.i. by immunohistochemistry and found increased levels of IFN-gamma, which was also inhibited by the denervation. Sham-operated animals exhibited similar responses as the nondenervated controls. Our data present for the first time very early kinetics for a cytokine gene expression during an experimental African trypanosomiasis. Furthermore, the data suggest a regulatory role for the autonomic nervous system on cytokine responses at both the mRNA and the protein levels.

Actinobacillus actinomycetemcomitans Immunosuppressive Protein Is a Member of the Family of Cytolethal Distending Toxins Capable of Causing a G2 Arrest in Human T Cells

We have previously shown that Actinobacillus actinomycetecomitans produces an immunosuppressive factor (ISF) capable of impairing human lymphocyte function by perturbing cell cycle progression. We now report that ISF is the product of the cdtB gene, one of three genes encoding the family of cytolethal distending toxins (Cdt). The ISF polypeptide exhibits ≥95% identity with Hemophilus ducreyi CdtB protein and ≤60% homology with Escherichia coli or Campylobacter jejuni CdtB. Pretreatment of PHA-activated lymphocytes with 5–25 ng ISF results in G2 arrest of CD4+ and CD8+ T cells. Similarly, treatment of HeLa cells results in G2 arrest and cell elongation and distension. However, lymphocytes are at least 5 times more sensitive to ISF than HeLa cells and do not undergo the elongation and distension that characterizes interactions of Cdts with cell lines. ISF-treated lymphocytes express normal cyclin A and B1 levels, but contain reduced levels of cell cycle-dependent kinase-1 (Cdk1). Additionally, the majority of Cdk1 is in the hyperphosphorylated, inactive, form. In contrast, PHA-induced G2 cells contain elevated levels of the hypophosphorylated, active Cdk1. Failure of ISF-treated cells to dephosphorylate Cdk1 is not associated with decreased availability of Cdc25. These studies suggest that the CdtB protein alone is capable of inducing G2 arrest in lymphocytes and cell cycle arrest, elongation, and distension of HeLa cells. Our studies also suggest that lymphocytes may be primary targets for A. actinomycetemcomitans CdtB (ISF) and possibly for other Cdt family members as well. Thus, Cdts may function to impair host immunity and contribute to the pathogenesis of disease associated with Cdt-producing organisms.

Antibody responses and body weights of chicken lines selected for high and low humoral responsiveness to sheep red blood cells. 2. Effects of separate application of Freund's Complete and Incomplete Adjuvant and antigen

Antibody (Ab) responses to SRBC, BSA, Mycobacterium butyricum, and Escherichia coli lipopolysaccharide (LPS) were measured in two chicken lines divergently selected for high and low Ab responses to SRBC, and in a randombred control line. Levels of Ab binding SRBC, BSA, and Mycobacterium protein, but not LPS were higher in the high Ab producing (H) line than in the control (C) and low Ab producing (L) lines (P < 0.05), and at almost every time, the L line showed significantly lower titers than the H and C lines. In the H and C lines, Ab responses to SRBC were enhanced when Complete Freund's Adjuvant (CFA) or Incomplete Freund's Adjuvant (IFA) were simultaneously administered on a separate location than SRBC. In the L line, Ab titers to SRBC and BSA were enhanced when antigen was administered emulsified in CFA. At all times until 28 d after sensitization the C and L line birds were significantly heavier than birds of the H line. Body weight, body growth, and percentage body growth were impaired in birds that received antigen emulsified in CFA, which suggested a negative relationship between BW gain and immune responses to Mycobacteria protein. Prolonged divergent selection for Ab responses to SRBC resulted into two lines that not only differ in Ab responses to T cell-dependent antigens but also in BW. In contrast to previous findings with the current lines, line differences with respect to Ab responses were not abolished by CFA treatment.

Identification and analysis of fipA, a Fusobacterium nucleatum immunosuppressive factor gene

We have previously demonstrated that sonic extracts of Fusobacterium nucleatum FDC 364 were capable of inhibiting human T-cell responses to mitogens and antigens. The purified F. nucleatum immunosuppressive protein (FIP) is composed of two subunits of 44 and 48 kDa. Furthermore, FIP inhibits T-cell activation by arresting cells in the middle of the G(1) phase of the cell cycle; the data available to date suggest that FIP impairs the expression of the proliferating-cell nuclear antigen. To initiate delineation of FIP structure-function relationships, molecular cloning of the FIP gene was carried out. A DNA library of F. nucleatum FDC 364 was constructed by partial digestion of genomic DNA with Sau3A and screened for the production of FIP with polyclonal antibody. Twelve immunoreactive clones were identified. One of these clones contained a 3.1-kbp insert and was chosen for further study. Cell lysates were found to contain an immunoreactive band that comigrated with the 44-kDa subcomponent of the native FIP. Sequencing of the 3.1-kpb insert revealed the presence of three open reading frames (ORFs). One ORF extends from nucleotides 415 to 1620, encodes 402 amino acids, and is preceded by a ribosome-binding site. Deletion analysis and antibody elution analysis showed that this ORF encodes the 44-kDa subunit (FipA) of native FIP. A second ORF is situated upstream of fipA. However, Northern (RNA) analysis suggested that fipA is not transcribed as part of an operon but transcribed from its own promotor. Finally, the partially purified recombinant FipA protein was capable of impairing T-cell activation in a manner consistent with the native protein. These results indicate that the two components that form the native protein are most probably distinct gene products and suggest that the 44-kDa FipA polypeptide is sufficient to mediate the immunosuppressive activities of the native protein complex.

Variation of Brucella abortus 2308 infection in BALB/c mice induced by prior vaccination with salt-extractable periplasmic proteins from Brucella abortus 19

The study compared the immune and protective responses induced in BALB/c mice vaccinated with six salt-extractable periplasmic protein fractions (Brucella cell surface proteins [BCSP]) of Brucella abortus 19 and later challenge exposed with B. abortus 2308. BCSP70 was precipitated with ammonium sulfate at 70% saturation, and BCSP100 was precipitated with ammonium sulfate at 100% saturation by use of supernatant fluid of BCSP70 that had been precipitated with 70% ammonium sulfate. Four subfractions were separated from BCSP100 by anion-exchange high-performance liquid chromatography (HPLC). Monophosphoryl lipid A (MPL) from Salmonella typhimurium Re mutant strain was used as a potential immune response modifier in some vaccines. Reduced or increased numbers of CFU and increased spleen size in the principal groups of mice relative to that of the nonvaccinated control group were considered protectiveness or virulence (survival) criteria. Results indicated that vaccines prepared from BCSP70 and BCSP100 were moderately protective and immunogenic. The subfractions designated BCSP100-A through BCSP100-D purified by anion-exchange HPLC were not protective when MPL was not used as an immune response modifier. However, two subfractions were associated with significant (P < 0.05) increases in CFU per spleen and splenomegaly in vaccinated mice compared with those in nonvaccinated challenge-exposed mice. MPL enhanced protection or was neutral when used with BCSP70, BCSP100, BCSP100-C, and BCSP100-D. Serologic results of an enzyme-linked immunosorbent assay indicated that MPL modulated the immunoglobulin G responses induced by BCSP70, BCSP100, and subfraction BCSP100-B vaccines only. The overall results suggest that certain proteinaceous periplasmic fractions might serve as virulence or survival factors in B. abortus infections.

Fusobacterium nucleatum inhibits human T-cell activation by arresting cells in the mid-G1 phase of the cell cycle

Fusobacterium nucleatum has been implicated in the pathogenesis of several diseases, including urinary tract infections, bacteremia, pericarditis, otitis media, and disorders of the oral cavity such as pulpal infections, alveolar bone abscesses, and periodontal disease. We have previously demonstrated that sonic extracts of F. nucleatum FDC 364 were capable of inhibiting human T-cell responses to mitogens and antigens. In this study, we have further characterized this immunosuppressive protein (FIP) and initiated experiments to determine its mode of action. The purified FIP has an apparent molecular mass of 90 to 100 kDa; sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates that the FIP is actually composed of two subunits with molecular masses of 48 and 44 kDa. Purified FIP retained its biological activity and was capable of inhibiting mitogen-induced proliferation of human T cells. Inhibition was dose dependent, and the FIP exhibited a specific activity approximately 250-fold greater than that of the crude extract. Cell cycle analysis indicates that FIP-treated cells were prevented from exiting the G0/G1 phase of the cell cycle. However, FIP did not alter the expression of activation markers (CD69, CD25, and CD71) or interleukin-2 secretion. The latter observations suggest that the T cells did indeed become activated and had entered the G1 phase of the cell cycle. Analysis of the expression of cyclins indicates that the phase of the cell cycle that is FIP sensitive resides somewhere beyond the restriction point of cyclin D2 (early to mid-G1) but prior to that of cyclins D3 and E (mid- to late G1). Finally, analysis of the expression of the proliferating cell nuclear antigen indicates that this is the earliest detectable defect in T cells exposed to FIP. We propose that if a block in the G1 phase of the cell cycle occurs in vivo in lymphocytes, it may result in a state of local and/or systemic immunosuppression. These suppressive effects could alter the nature and consequences of host-parasite interactions, thereby enhancing the pathogenicity of F. nucleatum itself or that of some other opportunistic organisms.

Reversal of lipopolysaccharide-analog-induced antibody suppression by anti-transforming growth factor beta and indomethacin

Monophosphoryl lipid A and a synthetic, nontoxic monosaccharide analog of lipid A, termed GLA 60, both strongly suppressed antibody production when administered 1 to 2 days prior to antigen. Evidence is presented that this suppression was mediated by two cytokines, prostaglandin E and transforming growth factor beta, because it was reversed by multiple injections of the cyclooxygenase inhibitor indomethacin and by in vitro addition of antibody to transforming growth factor beta.

Immune suppressive effects of Helicobacter pylori on human peripheral blood mononuclear cells

Helicobacter pylori, the causative agent of type-B gastritis and duodenal ulcer in man is described as a bacterium able to stimulate the human immune system. This study demonstrates that H. pylori besides this property possesses an immune suppressive activity. The in vitro proliferation of human peripheral blood mononuclear cells to purified protein derivative of tuberculin (PPD), phytohemagglutinin, and concanavalin A was reduced in a dose-dependent manner by bacteria which had been inactivated by incubation at 56 degrees C as well as by a soluble cytoplasmic fraction of H. pylori. The immune suppressive effect on the mitogen-induced proliferation could be increased by preincubation of the mononuclear cells with H. pylori. The observed effect does not seem to be a specific phenomenon depending on prior exposure of the blood donors to H. pylori, since suppression occurred with mononuclear cells of H. pylori-infected patients as well as of antibody-negative healthy control individuals. The suppressive activity was non-dialyzable, heat-labile (100 degrees C, 30 min) and sensitive to trypsin. Furthermore, the treatment at 100 degrees C caused an increase in the capability of H. pylori to induce lymphoproliferation. This fact indicates that the suppressive factor is also effective on H. pylori antigens. While exogenous interleukin-2, could to a certain extent, restore the responsiveness of the lymphocytes after PPD-stimulation in the presence of H. pylori, the addition of interleukin-1 had no effect on the suppressed lymphoproliferation. Cell-separation and cell-mixing experiments indicated that an influence on monocytes rather than on T cells is the major cause of the observed suppressive effect. Although the immunological mechanisms involved in H. pylori-associated gastritis are not clearly defined, it is reasonable to presume that suppression of host defense mechanisms may contribute to the pathogenesis of this disease.

Immunosuppressive effects of Prevotella intermedia on in vitro human lymphocyte activation

In this study, we have assessed four strains of Prevotella intermedia, isolated from periodontally involved lesions, for their ability to inhibit lymphocyte functions. All four strains were found to cause a dose-dependent inhibition of B- and T-cell proliferation in response to mitogens and antigens. This was reflected in altered DNA, RNA, and protein syntheses. Furthermore, P. intermedia appeared to affect the early stages of cell activation. This was ascertained by kinetic analysis in which it was determined that the extract had to be present during the first 24 h of incubation to cause suppression. Moreover, direct assessment of the early stages of cell activation indicated that release of cytokines and expression of the interleukin 2 receptor and CD69 on T cells were inhibited by P. intermedia sonic extracts. Finally, preliminary characterization of the immunosuppressive agent indicates that it has a molecular mass of approximately 50 kDa and is heat labile. It has been proposed that impaired host defense may play a pivotal role in the pathogenesis of many infections. The data presented in this paper suggest that microbially mediated immunosuppression may contribute to the pathogenesis of periodontal disease by altering the nature and consequences of host-parasite interactions.

Immune suppression induced by Actinobacillus actinomycetemcomitans: effects on immunoglobulin production by human B cells

Actinobacillus actinomycetemcomitans produces an immunosuppressive factor (ISF) which has been shown to suppress mitogen- and antigen-induced DNA, RNA, and protein synthesis in human T lymphocytes. In this study, we examined purified A. actinomycetemcomitans ISF for its ability to alter immunoglobulin production by human B cells. The ISF caused a dose-dependent inhibition of pokeweed mitogen (PWM)-induced immunoglobulin G (IgG) and IgM production. Preexposure to ISF was not required to achieve maximal inhibition of immunoglobulin synthesis, as previously observed for its effect on T-cell activation. Nevertheless, the ISF appeared to act by irreversibly affecting the early stages of cell activation. While PWM-induced immunoglobulin production is under the influence of T-regulatory circuits, it appears that the ISF interacts directly with B cells. First, ISF failed to alter either the synthesis of interleukin-2 (IL-2) or the expression of IL-2 receptors on T cells. Second, experiments in which individual purified populations of cells were exposed to ISF, washed, and placed back into tissue culture indicated that when all cells (i.e., T cells, B cells, and monocytes) were exposed to ISF, significant suppression was observed. However, when only one cell population was treated with ISF, suppression of both IgG and IgM synthesis was observed only when the B-cell-enriched population was exposed to ISF. These results in conjunction with our earlier findings suggest that the ISF functions via the activation of a regulatory subpopulation of B lymphocytes, which in turn either directly or indirectly (via suppressor T cells) downregulate both B- and T-cell responsiveness. Furthermore, it is hypothesized that patients who harbor A. actinomycetemcomitans could suffer from local or systemic immune suppression. This suppression may enhance the pathogenicity of A. actinomycetemcomitans itself or that of some other opportunistic organism.

Synergistic effects of locally administered cytostatic drugs and a surfactant on the development of delayed-type hypersensitivity to keyhole limpet haemocyanin in mice

The immunomodulating effects of two locally administered cytostatic drugs, the active cyclophosphamide-derivative Z 7557 and the plant alkaloid VP-16, were compared with the effects of systemically administered cyclophosphamide and several established adjuvants: Freund's complete adjuvant, dextran sulphate, and dimethyl dioctadecyl ammonium bromide (DDA). All agents tested promoted the development of delayed-type hypersensitivity (DTH) to keyhole limpet haemocyanin (KLH) in mice. Locally administered cytostatic drugs were the most effective immunostimulatory compounds, whereas DDA was the least toxic agent tested. In order to increase the effectiveness and/ or reduce the toxicity of these agents we tested the efficacy of combinations of cytostatic drugs and DDA to enhance DTH. The results show that DDA and suboptimal amounts of locally administered cytostatic drugs act synergistically on DTH.

Reduced proliferative response of mouse spleen cells to mitogens during infection with Salmonella typhimurium or Listeria monocytogenes

A significant reduction in the mitogenic responsiveness (uptake of 3H-thymidine) of murine spleen cells to concanavalin A, phytohemagglutinin or lipopolysaccharide was observed during infection with virulent Salmonella typhimurium. The decreased response to mitogens could be observed independent of the immunity to typhimurium (Ity) genotype, i.e. in CBA/J mice and C3H/HeJ mice (Ityr) as well as in C57BL/6 mice (Itys). Because reduced responsiveness was demonstrated in C3H/HeJ mice, which are susceptible to S. typhimurium infection but are unresponsive to lipopolysaccharide, it is concluded that the two phenomena are not correlated with one another. A similar decrease in response to mitogens was shown in mice infected with Listeria monocytogenes. Reduction in mitogenic responsiveness was directly correlated with the number of viable bacteria detected in the spleen cell suspension. Decreased lymphoproliferation could be observed as early as 2 days after infection and lasted 3 weeks in sublethally infected mice. The question remains whether or not the reduced responsiveness indicates an enhanced susceptibility to infection or merely represents a high degree of activation of defense mechanisms.

Immunosuppressive properties of Actinobacillus actinomycetemcomitans leukotoxin

Actinobacillus actinomycetemcomitans produces a leukotoxin that kills human polymorphonuclear cells (PMNs) and monocytes but not lymphocytes. In this study, we examined A. actinomycetemcomitans leukotoxin for its ability to alter human peripheral blood lymphocyte (HPBL) responsiveness. After a 90-min exposure to the leukotoxin, all monocytes were killed and HPBL responsiveness to mitogens and antigens was significantly inhibited. The ability of the leukotoxin to inhibit HPBL responses was not surprising, since monocytes and macrophages are required for many lymphocyte functions. However, we were unable to totally restore HPBL responsiveness when adherent autologous monocytes were added back to cultures of leukotoxin-treated lymphocytes. These studies demonstrate that A. actinomycetemcomitans leukotoxin may also exert nonlethal effects directly on lymphocytes. Furthermore, impaired lymphocyte function did not appear to be the result of indirect effects of products released by dying monocytes. Although it is not clear how A. actinomycetemcomitans acts to cause disease, several investigators have proposed that impaired host defenses may play a pivotal role. Several studies have demonstrated defects in PMN, monocyte, and lymphocyte function in patients with periodontal disease. These findings, along with the data presented in this paper, support the hypothesis that patients who harbor A. actinomycetemcomitans could suffer from local or systemic immune suppression. The effects of this suppression may be to enhance the pathogenicity of A. actinomycetemcomitans itself or that of some other opportunistic organism.

Immunosuppressive effects of Centipeda periodontii: selective cytotoxicity for lymphocytes and monocytes

We have examined soluble sonic extracts prepared from several strains of Centipeda periodontii for their ability to alter human lymphocyte function. These organisms were isolated from subgingival plaque of patients with periodontal disease. We found that sonicates from several, but not all, strains of C. periodontii caused a dose-dependent inhibition of lymphocyte responsiveness to concanavalin A, phytohemagglutinin, pokeweed mitogen, and formalinized Staphylococcus aureus. Inhibition was associated with a concomitant decrease in cell viability assessed by trypan blue exclusion, 51Cr release, and electron microscopy. The maximal number of dead cells was observed 20 to 24 h after exposure to the sonic extract. Susceptible cells include human lymphocytes (both B and T), monocytes, and erythrocytes, whereas polymorphonuclear cells, murine L-929 fibroblasts, and sheep erythrocytes were not affected. Preliminary characterization of the cytotoxic activity indicates that it is heat labile and trypsin sensitive and has an Mr of 60,000. It has been proposed that impaired host defense may play a pivotal role in the pathogenesis of periodontal diseases. The data presented in this paper suggest that immunosuppression (local or systemic or both) could be initiated by C. periodontii. This immunosuppression may alter the nature and consequences of host-parasite interactions, thereby enhancing the pathogenicity of C. periodontii itself or some other opportunistic organism.

Characteristics of DTH suppressor cells in mice infected with Candida albicans

Inoculation of 10(8) C. albicans intraperitoneally into Balb/c mice at given dosage was reported to induce suppression of antigen-specific delayed-type hypersensitivity. Adoptive transfer of spleen cells into normal syngeneic mice pre-treated with Cyclophosphamide confirmed the existence of suppressor cells in mice. Such cells were sensitive to treatment with anti-theta serum and complement, non-adherent to Sephadex G-10. A pretreatment of the mice with Cyclophosphamide eliminated DTH suppression. Treatment with antimacrophage agents via intraperitoneal abrogated suppression only if being effected before inoculation of alive 10(8) Candida albicans. It is concluded that the spleen suppressor cell is a T-lymphocyte whose precursor is Cyclophosphamide-sensitive, requiring the macrophage to be induced.

Stimulation of murine lymphocyte blastogenesis by mitogens in heat-killed Histoplasma capsulatum yeast cells

In vitro blastogenesis by normal murine splenocytes from several mouse strains has been detected after exposure to heat-killed Histoplasma capsulatum yeast cells. Maximal lymphocyte stimulation induced by 10(4) heat-killed cells resulted in 20- to 45-fold increases in [3H]thymidine uptake by splenocytes when compared with responses by normal unstimulated lymphocytes. The kinetics for this response to heat-killed H. capsulatum cells has shown peak mitogenesis 3 days after culture. Examination of the mitogenic potential of soluble antigen preparations from H. capsulatum has revealed stimulation of lymphocyte blastogenesis with yeast cell sonicates and autolysates but not substances from autoclaved yeast cells. The levels of lymphocyte blastogenesis induced by sonicates or autolysates were comparable to mitogen responses stimulated by heat-killed cells. Preliminary biochemical characterization of the mitogenic factor(s) associated with yeast cell sonicates show two peaks of activity, at 178,000 and less than 12,000 Mr, which have a protein or glycoprotein nature. Finally, analysis of lymphocyte blastogenesis in cultures enriched for selected lymphocyte subpopulations has shown that T lymphocytes are preferentially stimulated by yeast cell mitogens.

Regulation of herpes simplex virus-specific cell-mediated immunity by a specific suppressor factor

Our study was designed to investigate the nature of an antigen-specific suppressor factor generated by antigen-stimulated herpes simplex virus (HSV)-immune splenocytes. Factor SF-200, a 90,000- to 100,000-dalton fraction obtained after Sephacryl gel filtration, suppressed the generation of HSV-specific cytotoxic T-lymphocyte and lymphoproliferative responses. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis of SF-200 indicated that it contained an I-J+, anti-idiotypic protein. It was possible to adsorb the suppressor activity of SF-200 to an anti-I-J immunoaffinity column. The suppressor activity could be eluted from the immunoaffinity column with a low-pH buffer. The acid-eluted material was determined to be both I-J+ and reactive with anti-HSV antiserum by Western blot analysis. Both SF-200 and the I-J+ suppressor activity suppressed only HSV-specific cell-mediated immunity responses. However, it was possible to generate nonspecific suppressor activity by incubating the I-J+ suppressor factor with Lyt 1+ splenocytes from HSV-immune mice. The implication of these results with respect to the model for a suppressor cell circuit regulating HSV-specific cell-mediated immunity responses is discussed.

Characterization of a phase I Coxiella burnetii chloroform-methanol residue vaccine that induces active immunity against Q fever in C57BL/10 ScN mice

The effect of phase I Coxiella burnetii chloroform-methanol residue vaccine (CMRV) on the response of murine splenic lymphocytes to mitogenic and antigenic stimuli was evaluated in C57BL/10 ScN endotoxinnonresponder mice with an in vitro lymphocyte proliferation assay. Intraperitoneal injection of phase I CMRV resulted in antibody production against phases I and II antigens. Lymphocytes were responsive in vitro to concanavalin A, phytohemagglutinin, pokeweed mitogen, and specific recall antigens. Antibodies against phases I and II antigens were not detected after intraperitoneal injection of chloroform-methanol extract (CME). Lymphocytes also were only slightly hyporesponsive to mitogens. Reconstitution of the CMRV with the CME of phase I whole cells restored the immunopathological reactions that were associated with the phase I whole cell vaccine (WCV). The CMRV was more mitogenic than the WCV for lymphocytes from mice injected with saline. Lymphocytes from phase I WCV-injected mice were negatively modulated with nontoxic concentrations of homologous WCV or CMRV. Lymphocytes from phase I CMRV-injected mice were only slightly hyporesponsive to mitogens and were significantly stimulated by antigens of either WCV or CMRV as recall antigens. Vaccination of mice with 100 micrograms of CMRV, CME, or WCV provided 80, 0, or 50% protection, respectively, against a lethal intraperitoneal challenge with viable phase I C. burnetii. The epitopes which induce immunological hyporesponsiveness, negative modulation, and the death of lymphocytes were fractionated into the CMRV and CME. The CMRV provides at least one of the determinants which induce immunosuppression, whereas CME contains specific or nonspecific components or both. Collectively, these results show that the CMRV may be a potential candidate to replace the WCV currently used for human vaccination.

Suppression of cellular immunity to Listeria monocytogenes by activated macrophages: mediation by prostaglandins

We previously demonstrated the suppression of cell-mediated immunity to Listeria monocytogenes by Pseudomonas aeruginosa-induced, macrophage-like cells. The present study was undertaken to evaluate the mechanism for this suppression. P. aeruginosa supernatant was shown to activate macrophages by the criteria of increased bactericidal capacities and increased attachment to glass surfaces. Acquired cellular resistance to L. monocytogenes could also be inhibited by macrophages from L. monocytogenes-pretreated mice. The depression of acquired immunity by P. aeruginosa- or L. monocytogenes-activated macrophages did not appear to be due to a reduction of antigenic stimulus after nonspecific macrophage activation. In contrast, our findings suggest that suppression is mediated by activated macrophages through a prostaglandin-dependent mechanism. In vivo administration of aspirin blocked the immunosuppressive effect of P. aeruginosa- or L. monocytogenes-activated cells. Moreover, the suppressive activity of supernatants of macrophages from Listeria-infected mice was reversed when indomethacin was present during supernatant generation. Finally, prostaglandin E1 treatment in vivo profoundly inhibited the induction of cell-mediated immunity to L. monocytogenes. The possible role and mechanism of prostaglandin in suppressing cellular immunity to intracellular bacteria are discussed.

Chemical properties and immunobiological activities of streptococcal lipoteichoic acids

Lipoteichoic acids (LTAs) were chromatographically purified from crude phenol-water extract of whole cells of some streptococcal species, which included Streptococcus pyogenes Sv, Streptococcus mutans 6715, and Streptococcus sanguis ATCC 10556. Among these, special attention was paid to S. pyogenes LTA for analyses of chemical composition and biological activities. All LTA preparations contained equimolar amounts of glycerol and phosphorus. Chemical analyses showed that S. pyogenes LTA contained glycerophosphate, alanine, glucose, and fatty acids (as palmitic acid) at molar ratio of 1 : 0.1 : 0.1 : 0.25. The crude phenol-water extract and isolated LTA from S. pyogenes Sv were found to be mitogenic for spleen cells of BALB/c and BALB/c (nu/nu) mice, but not for thymus cells of BALB/c mice. The mitogenicity of deacylated LTA (dLTA) was significantly lower than that of LTA. It was also found that various LTA preparations possessed polyclonal B cell activation ability and adjuvant activity both in vivo and in vitro, as demonstrated by using hemolytic plaque assay. LTA, but not dLTA, induced macrophage activation which resulted in tumor cytotoxicity in mice. Limulus lysate activity of S. pyogenes LTA was approximately 1,000 fold lower than that of Escherichia coli lipopolysaccharide. These results indicate that streptococcal LTA possesses various immunobiological activities that modulate lymphoreticular system in vivo and in vitro.

Decreased delayed-type hypersensitivity and increased protection to Listeria monocytogenes seen in mice infected with mucoid and nonmucoid Pseudomonas aeruginosa

Infection of mice with Pseudomonas aeruginosa, washed and unwashed, mucoid and nonmucoid, altered subsequent immunity to Listeria monocytogenes. Mice were protected against lethal doses of L. monocytogenes yet exhibited decreased delayed-type hypersensitivity footpad swelling to sublethal doses. The mucoid coating of mucoid P. aeruginosa, an important pathogen in chronic bronchopulmonary disorders, imparted no additional immunomodulating capabilities to P. aeruginosa.

Effects of a Fusobacterium nucleatum extract on immunoregulation in mice

The purpose of this study was to examine the effect of an extract of Fusobacterium nucleatum on humoral and cell-mediated immunity and phagocyte functions in mice. The extract was obtained from the heat-inactivated supernatant of sonicated F. nucleatum. Mouse splenocytes were cultured with sheep red blood cells (SRBC), and antibody formation was assayed by counting the plaque-forming cells (PFC). After C3H mouse skin was grafted onto the BALB/c mouse, cytotoxicity of BALB/c mouse splenocytes to L-cells was enumerated, T- and B-cell blastogenesis was determined by the uptake of 3H-thymidine. In vivo phagocyte functions were measured using carbon clearance test, bactericidal, and acid phosphatase activity assays. The number of SRBC-specific and non-specific PFC in splenocytes stimulated with the extract increased 2.5-8.7-fold over that of unstimulated splenocytes. Cytotoxicity of splenocytes from the extract-injected mice decreased in a dose-dependent fashion at 12 days after grafting. T-cell mitogenicity of the extract was observed. The carbon clearance rate was reduced, and bactericidal and acid phosphatase activities were elevated by the extract injection of the mice. In conclusion, F. nucleatum extract has an adjuvant effect on humoral immunity, and a suppressive effect on cell-mediated immunity and activated phagocyte functions.

Modification of immune induction by adjuvant

The role of adjuvanticity in the modification of the immune induction was studied by separate application of antigen and adjuvant in mice. An antigen specific plaque forming cell (PFC) test and a delayed type hypersensitivity (DTH) assay were used for these studies. Antigen (SRBC) and adjuvant were applied separately in time and place. A stable well defined water-in-oil emulsion without antigen was used as adjuvant. Our studies have shown that intraperitoneal (i.p.) injection of this adjuvant stimulates the intravenous (i.v.) induced PFC response, while the DTH response is suppressed. This effect can be demonstrated even when adjuvant has been injected i.p. 5 days prior to i.v. antigen injection. The stimulation of the PFC response depends on the dosage of i.v. injected antigen.

Chemistry of immunomodulators

A large number of synthetic derivatives, inorganic compounds or naturally occurring substances are able to depress, regulate or enhance the immune response. Immunomodulators, among which some are chemically well defined and others are complex preparations, exhibit a great variety of chemical structures which are briefly reviewed, without details on their immunopharmacological properties. These molecules allow access to a new type of therapy which aims at acting on the host defense mechanisms.

Suppression of in vitro lymphocyte proliferation in C57BL/10 ScN mice vaccinated with phase I Coxiella burnetii

The effect of inactivated phase I and phase II Coxiella burnetii whole cell vaccine (WCV) on the response of murine spleen cells to mitogenic and antigenic stimuli was evaluated in C57BL/10 ScN endotoxin nonresponder mice with an in vitro lymphocyte proliferation assay. Intraperitoneal injection of phase I WCV into mice resulted in marked and persistent suppression of the proliferative response of spleen cells to concanavalin A, phytohemagglutinin, and pokeweed mitogen. This response was time and dose dependent and was not associated with decreased lymphocyte viability. By using a standard dose of 100 micrograms of phase I WCV, suppression of mitogenic responsiveness was first detected 3 days postinjection, attained maximum levels by day 14, and persisted for longer than 5 weeks. Suppression of mitogenic lymphocyte proliferation also was demonstrated after inoculation of animals with viable phase I organisms. The observed hyporesponsiveness of spleen cells from phase I WCV-injected animals was not either the result of a shift in the mitogenic dose optimum or due to a change in the day of in vitro peak response. Spleen cells from phase I WCV-injected mice were negatively regulated with homologous antigen. Investigation of the mechanism of action of phase I WCV, with a 51Cr-release assay, and trypan blue dye exclusion showed that phase I WCV was not directly cytolytic or cytotoxic to spleen cells from normal or vaccinated mice. Phase II WCV did not induce significant mitogenic hyporesponsiveness or negative modulation of spleen cells. These findings extend the observations of adverse host responses associated with the phase I WCV and underscore the need to develop a microbial fraction which possesses protective potency but which lacks the propensity to induce deleterious tissue reactions and immunosuppression.

Specific humoral depression in chronic patients infected by Trypanosoma cruzi

Realizamos um estudo comparativo entre o xenodiagnóstico e os testes sorológicos para a doença de Chagas. Cento e cincoenta pacientes de algumas áreas endêmicas foram estudados. Quatro deles pareceram revelar um estado particular com um xenodiagnóstico positivo e uma sorologia negativa, esta realizada com quatro diferentes técnicas clássicas (teste de immunofluorescência, ELISA: Enzyme Linked Immunosorbent Assay, teste de fixação do complemento e teste de immuno-eletroforese). O soro de um dos pacientes que apresentou depressão humoral específica mostra elevada quantidade de antígenos circulantes comprovada pela técnica da immuno-eletroforese. Os Autores sugerem o uso de um teste sorológico para detectar a presença de antígenos circulantes de T. cruzi, além da utilização de testes sorológicos clássicos. Isto permitiria o diagnóstico da doença de Chagas em pacientes com uma baixa (ou mesmo inexistente) produção de anticorpos específicos.

Modulation of in vitro human lymphocyte responses by an exopolysaccharide from Capnocytophaga ochracea

An exopolysaccharide (EP), purified from spent culture fluid previously inoculated with Capnocytophaga ochracea strain 25, suppressed in vitro human peripheral blood lymphocyte responses to the mitogen concanavalin A. EP was suppressive when added to cultures before the mitogen, but enhanced responses when added 24 or 48 hr after the mitogen.

Suppression of murine lymphocyte mitogen responses by exopolysaccharide from Capnocytophaga ochracea

An extracellular polysaccharide was purified from culture supernatants of Capnocytophaga ochracea 25, a gram-negative bacillus associated with human periodontal disease. The extracellular polysaccharide suppressed in vitro mitogenic responses of murine splenic lymphocytes to concanavalin A and lipopolysaccharide. This suppression wad dose dependent, persisted up to 120 h, and was not caused by direct toxicity of the extracellular polysaccharide.

Depression by Pseudomonas aeruginosa of two T-cell-mediated responses, anti-Listeria immunity and delayed-type hypersensitivity to sheep erythrocytes

Pseudomonas aeruginosa was studied for its effects on T-cell-mediated responses in mice, as exemplified by anti-Listeria immunity and delayed-type hypersensitivity to sheep erythrocytes. Immunity to Listeria monocytogenes was measured by quantitation of bacteria in spleens and mortality; delayed hypersensitivity to sheep erythrocytes was tested by the footpad reaction. Three different preparations of P. aeruginosa were used: the supernatant of a heat-killed culture, living bacteria, and heat-killed organisms. Similar results were obtained with the three preparations. Administration of P. aeruginosa 24 h before Listeria infection reduced the resistance to the secondary challenge, as measured by increased bacterial multiplication in the spleen and rate of mortality. Cell transfer experiments showed that pretreatment of normal recipient mice with P. aeruginosa prevented them from being adoptively immunized against a Listeria challenge infection with spleen cells from immune donors. They also showed that treatment of donors with P. aeruginosa before immunization affected the capacity of their spleen cells to protect normal recipients against Listeria. Furthermore, spleen and peritoneal exudate cells obtained from mice given P. aeruginosa were capable of preventing immunization of normal recipients against Listeria. Similar results were obtained when the delayed hypersensitivity response to sheep erythrocytes was studied. The suppressive activity of P. aeruginosa-treated spleen cells was lost by removing adherent cells. Conversely, the adherent, heat-killed, anti-immunoglobulin-treated spleen cells exerted a suppressor effect. It thus appears that P. aeruginosa injection changes macrophage and T-lymphocyte activities and results in the development of adherent, macrophage-like suppressor cells in the spleen and peritoneal cavity.

Modulation of the host immune response as a result of Chlamydia psittaci infection

After intraperitoneal injection of mice with infectious, inactivated, or envelope preparations of the elementary body of Chlamydia psittaci, lymphocyte transformation of spleen cells to the mitogens concanavalin A, phytohemagglutinin, and lipopolysaccharide was significantly reduced 1 and 2 weeks postinjection. Lymphocyte response returned to the control values by 4 weeks. Similarly, transformation of cells by chlamydial antigen was not detected until 4 weeks postinjection. Injection of the noninfectious intracellular reticulate body, in contrast, had little effect on transformation of cells to concanavalin A. When control spleen cells were incubated with infectious or inactivated elementary bodies in vitro, response to all three mitogens was also reduced. The sooner the organisms were added after the addition of mitogen, the greater the reduction in transformation. Incubation with elementary body envelopes and reticulate bodies had no effect on lymphocyte transformation of the spleen cells to concanavalin A. The relationship between the observed ability to reduce the response in the in vitro assay of lymphocyte transformation and the actual in vivo establishment of infection is discussed.

Mitogen- and viral antigen-induced transformation of lymphocytes from normal mink and from mink with progressive or nonprogressive Aleutian disease

Peripheral blood lymphocytes (PBL) from mink with progressive Aleutian disease (AD) were shown to be significantly less responsive to phytohemagglutinin, concanavalin A, and pokeweed mitogen than were PBL from normal mink and from mink with a nonprogressive form of AD. Response to the virus of AD was significantly greater in PBL cultures from mink with nonprogressive AD than in those from normal mink or mink with progressive AD. After experimental infection with AD virus, mink PBL were responsive to viral antigen only transiently. These findings suggest that lymphocyte responsiveness as indicated by transformation induced by mitogens or viral antigen may be an important aspect of host response to infection with the parvovirus of AD.

Nonspecific immunodepression and protective immunity in mice infected with Leishmania mexicana

C57BL/6 mice infected with Leishmania mexicana showed depression of the in vitro immunoglobulin M-plaque-forming cell response to sheep erythrocytes. Immunodepression was present 3 weeks after inoculation and was maximal at 11 weeks. Thereafter, there was a gradual return to normal immunoresponsiveness correlated with the resolution of lesions. At the time of maximal immunodepression, spleen cells from infected mice diminished the plaque-forming cell response to sheep erythrocytes of normal spleen cells. On the other hand, specific responses, as exemplified by protective immunity to a challenge infection and delayed hypersensitivity responses to parasite antigens, were apparently unaffected. These responses were both present in mice bearing primary lesions and were maximal in recovered mice. The significance of these findings is discussed in relation to a current hypothesis on parasite-induced immunodepression.

Antigenic modification: its relation to protective host resistance in murine salmonellosis

Both the physical state of the immunogen and the route of immunization were found to be extremely important in inducing effective host resistance against salmonellosis.

Dipetalonema viteae infective larvae reach reproductive maturity in rats immunodepressed by prior exposure to Schistosoma mansoni or its products and in congenitally athymic rats

Infective larvae of Dipetalonema viteae did not reach maturity in inbred Fischer rats. However, female adults of D. viteae when transplanted surgically into Fischer rats established and the resulting microfilaraemia from the transplanted worms persisted for about 120 days after infection. Sequential dissections showed that some of the female worms transplanted remained viable in rats for about 35 days after infection. After inoculation of infective larvae into rats a varying number transformed into stage-4 larvae but they did not develop into adult worms and were killed. However, when the rats were immunodepressed non-specifically by a pre-existing Schistosoma mansoni infection or by treatment with S. mansoni-derived substance(s), a number of stage-4 larvae renewed their development and reached sexual maturity. These worms produced microfilariae which were observed in the peripheral blood for about 40 days. The effect of previous infection with S. mansoni on the survival and growth of D. viteae in Fischer rats depends greatly on the relative timing of infection because infective larvae of D. viteae reached maturity only when rats were inoculated with infective larvae after 15 days of S. mansoni infection but not after 21 or 28 days of S. mansoni infection. D. viteae will also develop to maturity in congenitally athymic rats. In congenitally athymic rats (Nu/Nu) each given 75 infective larvae, both the microfilaraemia and adult worm recovery at post-mortem were higher than those which resulted in Nu/Nu rats given an infection of 200 larvae. These experiments show that in rats innate immunity to this filarial nematode reflects a very rapidly induced acquired immunity which kills the parasite before it reaches maturity.

Immunosuppression of anti-sheep erythrocyte responses by glycerol teichoic acid immune complexes

Sprague-Dawley rats which produce "naturally occurring" antibodies to glycerol teichoic acid (GTA) displayed immunosuppression of anti-sheep erythrocyte plaque-forming cell and serum antibody responses when a single dose of lipid-free GTA was administered 24 h before immunization. Such suppression was enhanced by administering GTA complexed with anti-GTA immunoglobulin G. Animals fed a GTA-free diet produced no anti-GTA immunoglobulins and failed to show GTA-mediated immunosuppression under similar experimental conditions. However, when those animals were given GTA-anti-GTA complexes, suppression was evident. The results suggested antigenic competition mediated by immune complex-activated suppressor T cells. Lipid-free GTA did not stimulate serum antibody responses under the experimental conditions employed.

Molecular characterization of receptor binding proteins and immunogens of virulent Treponema pallidum

Receptor binding proteins of Treponema pallidum were identified by incubation of [35S]methionine-labeled, soluble T. pallidum preparations with formaldehyde-fixed HEp-2 cells. Three major treponemal proteins (bands 1--3) that avidly bound to the eucaryotic cell surface were detected by sodium dodecylsulfate-polyacrylamide gel electrophoresis and fluorography. Brief trypsin treatment of HEp-2 cells before formaldehyde fixation reduced the extent of the interaction of these treponemal macromolecules, which implicated receptor-mediated attachment mechanisms. The presence of unlabeled T. pallidum preparations directly competed with radiolabeled T. pallidum samples for the available HEp-2 cells, which suggested a limiting number of membrane binding sites. Samples of unlabeled avirulent Reiter treponeme did not compete. T. Pallidum immunogens were examined by radioimmunoprecipitation with human and rabbit syphilitic sera. Of interest were the similarities and extent of the humoral response represented by the detection of antigen-antibody complexes against numberous treponemal proteins, including bands 1--3. T. pallidum portein band 1 appeared to be the major antigenic stimulus. Formation of antigen-antibody complexes between 35S-labeled T. pallidum proteins and human syphilitic sera was prevented by unlabeled T. pallidum but not by T. phagedenis preparations, which demonstrated specificity of the reaction. Gel profiles of radioimmunoprecipitation assays using radiolabeled T. pallidum antigens and human syphilitic and yaws sera delineated both the similarities and differences in the humoral response to these two spirochetes. The latter suggested both overlapping and distinguishing antigenic properties between T. pallidum and T. pertenue. Detection in yaws sera of specific antibody against T. pallidum protein bands 1--3 further incriminates the role of these three treponemal proteins as virulence determinants.

Relationships between adjuvant, immunosuppressive, and mitogenic activities of staphylococcal peptidoglycan

Staphylococcal peptidoglycan (PG) possesses in vivo immunodulating activity and is a B-cell mitogen in mice. The effect of PG on in vitro immune response of mouse splenocytes to sheep erythrocytes (SRBC) was studied, as well as the relationships between in vivo and in vitro adjuvant, immunosuppressive, and mitogenic activities of PG in terms of dose response, time kinetics, and physical state. Particulate PG suppressed in vivo anti-SRBC response when injected in a large dose before or simultaneously with SRBC. A small dose of particulate PG given before or along with the antigen was immunostimulatory. Soluble PG was adjuvant active in both high and low doses when injected before or along with the antigen. Both PG preparations were adjuvant active for mouse splenocytes in vitro immunized with SRBC, but particulate PG was more active. Even high doses of particulate PG were not directly suppressive for the in vitro immune response. Particulate PG was also mitogenic for mouse splenocytes, and the maximum increase in [3H]thymidine incorporation was observed after 2 days of culture. Soluble PG was not mitogenic during the 5-day incubation period. These results indicate that the physical state of PG, its dose, and its time of application are important factors determining its immunomodulating and mitogenic activities, and that by changing them it is possible to dissociate the adjuvant, immunosuppressive, and mitogenic properties of PG.

Evidence for the synthesis and release of strongly immunosuppressive, noncytotoxic substances by Streptococcus intermedius

Products secreted by Streptococcus intermedius were studied for their effects on the immune response. Three different preparations of crude extracellular products from S. intermedius (CEP-Si) were found to have powerful suppressor activity in vitro as shown by inhibition of human lymphocyte proliferation (uptake of [3H]thymidine) and protein synthesis in response to a wide variety of stimulants, including mitogens and antigens, and suppression of plaque formation by human cells in response to sheep erythrocytes. CEP-Si was noncytotoxic, because cells incubated with high concentrations of CEP-Si and subsequently washed were viable and recovered their ability to respond to mitogens, and because leukocyte migration was not inhibited by CEP-Si, nor was the release of leukocyte migration inhibitory factor from sensitized lymphocytes. The possibility of antigen or mitogen competition was excluded. The effects of CEP-Si in vitro were time dependent and did not require the presence of monocytes. Cells pretreated with CEP-Si and then washed suppressed plaque formation by fresh autologous cells in highly stimulated cultures. CEP-Si injected into C57BL/6 mice also strongly suppressed their immune response to sheep erythrocytes, and the in vivo suppression was correlated with the effects of CEP-Si in vitro.

Modulation of the immune response to sheep erythrocytes by lipid-free glycerol teichoic acid

The 4-day response of C3H/HeJ mice to sheep erythrocytes was suppressed by a lipid-free teichoic acid with an average molecular weight of 2,900 when it was administered by the intraperitoneal route. Enhancement was not observed at that time, and neither suppression nor enhancement could be demonstrated by the intravenous route. Either suppression or enhancement of background plaques could be induced, depending upon the timing. Dosage influenced the degree of suppression from 8 to 100 micrograms, whereas suppression of background plaques required only 1 microgram of lipid-free teichoic acid. The kinetics of the sheep erythrocyte response was altered by treatment of the mice with lipid-free teichoic acid, delaying the peak until day 5 and producing enhancement at that time. Although lipid-free teichoic acid was shown to be toxic for mouse splenocytes (50% lethal dose, ca. 200 micrograms) in vitro, no effect at the levels employed was observed in vivo. The data presented indicate that modulatory activity is influenced by route, timing, dosage, and apparently the number of antibody-secreting cells.

Pseudomonas aeruginosa infection depresses contact sensitivity to oxazolone by enhancing suppressor cell activity

The depression of contact sensitivity to oxazolone in mice infected with Pseudomonas aeruginosa was studied. In oxazolone-sensitized mice, P. aeruginosa infection affects cell proliferation in the lymph nodes draining the site of sensitization. This impaired cell proliferation does not seem to be due to an altered lymphocyte reactivity, since lymph node and spleen cells from infected animals show a normal mitotic responsiveness to both T and B cell mitogens. In addition, the draining lymph nodes and spleens of mice exhibiting a depressed response to oxazolone contain a cell population able actively to suppress the response to the same antigen of syngeneic recipients sensitized immediately before the cell transfer. These suppressor cells require antigenic stimulation and appear to act on the induction phase of contact sensitivity.