Depression of the antibody response in Pseudomonas aeruginosa-injected mice

Serum antibody response to Pseudomonas aeruginosa antigens during corneal infection

Previous studies in our laboratory have indicated that naturally resistant, inbred DBA/2J mice mount a greater serum antibody response to Pseudomonas aeruginosa 19660 than susceptible C57BL/6J mice. However, the specificity of the antibody produced was not known. The present study examines the specificity and kinetics of the humoral response of these mouse strains to potential virulence factors produced by the organism during both a primary and a secondary corneal infection administered 4 weeks after the primary infection. Serum antibody levels specific for lipopolysaccharide (LPS), exotoxin A, phospholipase C (PLC), alkaline protease, elastase, and flagella were measured by enzyme-linked immunosorbent assay. Little or no antibody to either alkaline protease or elastase was detected during either primary or secondary infection. Immunoglobulin G (IgG) antibodies specific to exotoxin A, PLC, and flagella were detected 2 weeks after primary infection, and a rapid response to these antigens was measured 1 week after secondary infection. During primary infection, detectable LPS-specific antibody was only IgM, while IgG appeared only after secondary infection. The kinetics of the humoral response in susceptible C57BL/6J mice were similar to those in resistant DBA/2J mice, although the magnitude of the response varied according to the antigen tested. These results indicate that LPS, exotoxin A, PLC, and flagella are present or produced in amounts that are immunogenic during corneal infection by P. aeruginosa 19660 in the mouse strains tested.

Selective impairment of B cell function by Neisseria meningitidis

Spleen cells from CBA/J mice infected with Neisseria meningitidis displayed depressed in vitro plaque-forming cell (PFC) responses to T-dependent (sheep red blood cell; SRBC) and T-independent (TNP-LPS, TNP-Ficoll) antigens. The inhibition was observed over a wide range of antigen concentrations. The decreased responsiveness of splenocytes from infected mice was due to a selective impairment of B-cell function since helper-T-cell activity was intact in infected mice as shown by the ability of T-enriched lymphocytes to cooperate with normal B-enriched lymphocytes in the generation of an anti-SRBC response, accessory macrophage function was preserved since adherent spleen cells from bacteria-injected mice were shown to produce normal or increased levels of IL-1 and were able to cooperate with normal non-adherent spleen cells in the generation of PFC against SRBC. Addition of peritoneal cells from normal animals or extraneous IL-1 both failed to restore normal PFC responses in cultures of splenocytes from infected mice. Finally, B-enriched lymphocytes from infected mice produced poor anti-SRBC responses when cultured with either Con A supernatant or T-enriched lymphocytes from normal or infected mice. Cell-mixing experiments failed to detect the presence of suppressor cells in cultures of unfractionated spleen cells or B-enriched lymphocytes from infected mice. Therefore, the immunological unresponsiveness associated with a Neisseria meningitidis infection was attributed to a meningococcus-induced defect(s) in B-cell function. In vivo polyclonal B-cell activation leading to clonal exhaustion did not play a major role in the depression of humoral responses since meningococcal infection induced little or no polyclonal Ig secretion.

Immunomodulation in mice by experimental infection with Yersinia enterocolitica

Intraperitoneal infection of mice with two strains of Yersinia enterocolitica resulted in an inflammatory response and immunomodulation which appeared to be related to the invasive properties of the bacteria. The primary antibody response to sheep erythrocytes was enhanced by noninvasive cultures of Y. enterocolitica (serotype O:4-33 grown at 22 C and at 37 C, and serotype O:3 grown at 37 C), when given at the same time or two days after the antigen (invasiveness was tested on HeLa cells). In contrast, invasive cultures of serotype O:3 grown at 22 C, injected three days before the antigen suppressed the antibody response; enhancement was caused by these cultures only when given on the day of immunization. Delayed-type hypersensitivity to sheep erythrocytes was also suppressed by invasive cultures of Y. enterocolitica. These data indicate that the temperature of growth as well as some serotype-linked factors play a role in immunomodulation by Y. enterocolitica.

Activation of murine B lymphocytes by Neisseria meningitidis and isolated meningococcal surface antigens

Heat-killed Neisseria meningitidis was found to be a potent mitogen for mouse splenic lymphocytes. Results obtained with different cell separation techniques indicated that the bacteria acted to selectively induce proliferation of B lymphocytes. First, partial or total depletion of T lymphocytes by treatment with various anti-T-cell antisera plus complement did not affect the ability of the remaining spleen cells to proliferate in response to N. meningitidis. Second, T lymphocytes purified by affinity chromatography through an immunoglobulin-antiimmunoglobulin-coated glass bead column were unresponsive to meningococcal stimulation, even when provided with a source of macrophages (irradiated or mitomycin C-treated spleen cells). Finally, treatment of spleen cells with soy bean agglutinin showed that, whereas the soy bean agglutinin-positive population (B-enriched lymphocytes) was highly responsive to stimulation by N. meningitidis, the soy bean agglutinin-negative population (T-enriched lymphocytes) displayed only a background level of proliferation when exposed to the bacteria. Isolated meningococcal surface antigens such as lipopolysaccharide (LPS) and outer membranes also possessed mitogenic activity and induced proliferation of B lymphocytes in a dose-dependent manner. Both LPS and non-LPS components contributed to the mitogenicity of outer membranes since the addition of outer membrane preparations to spleen cells from the low LPS responder C3H/HeJ mouse strain gave rise to a high level of proliferative activity.

Evidence for autoantibody production associated with polyclonal B-cell activation by Pseudomonas aeruginosa

Experimental infection of mice with Pseudomonas aeruginosa resulted in the polyclonal activation of B lymphocytes, as assessed by the spontaneous plaque-forming cell (PFC) response to trinitrophenyl and sheep erythrocytes. Additionally, a PFC response to bromelain-treated syngeneic erythrocytes (Br-MRBC) could be detected in infected mice, suggesting that P. aeruginosa infection might also induce activation of self-reactive B-cell clones and consequently lead to autoantibody production. Furthermore, in cultures of mouse peritoneal cells, heat-killed P. aeruginosa enhanced the development of anti-Br-MRBC PFC, even under conditions where cell division was blocked, suggesting that the in vitro P. aeruginosa-induced enhancement of anti-Br-MRBC PFC was essentially related to cell differentiation, cell division playing only a minor role. The mechanism of the in vivo and in vitro P. aeruginosa-induced activation of anti-Br-MRBC PFC are discussed.

Mouse footpad infection by Pseudomonas aeruginosa: evidence for delayed hypersensitivity to specific bacterial antigen

Mouse hind footpad inoculation with 1 x 10(7) viable Pseudomonas aeruginosa cells produces a long-lasting, self-limiting disease process characterized by a bacterial multiplication that parallels the swelling of the infected footpad. Regional popliteal and inguinal lymph nodes and spleen of infected animals show cellular modifications which are almost entirely due to lymphocyte proliferation, as indicated by sponteneous DNA synthesis experiments in vitro. Furthermore, mice which had been infected in their footpad either 20 or 27 days previously and challenged with P. aeruginosa antigens into the controlateral footpad show, 24 h later, a marked increase in regional popliteal lymph node weight, indicating the development of delayed hypersensitivity to Pseudomonas antigens.