Alteration of murine immune response by Pseudomonas aeruginosa exotoxin A

In silico integrative analysis predicts relevant properties of exotoxin-derived peptides for the design of vaccines against Pseudomonas aeruginosa

Pseudomonas aeruginosa (PA) is an opportunistic human pathogen responsible for causing serious infections in patients with cystic fibrosis. Infections caused by PA are difficult to treat and eradicate due to intrinsic and added resistance to antibiotic therapy. Therefore, it is necessary to establish effective prevention strategies against this infectious agent. In this study, a combination of immunoinformatic tools was applied to predict immunogenic and immunodominant regions in the structure of exotoxins commonly secreted as virulence factors in PA infection (ExoA, ExoS, ExoT, ExoU and ExoY). The peptides derived from exotoxins were evaluated for the potential affinity for human leukocyte antigen (HLA) I and HLA-II molecules, antigenicity score and toxicity profile. From an initial screening of 941 peptides, 13 (1.38%) were successful in all analyzes. The peptides with relevant immunogenic properties were mainly those derived from Exo A (10 / 76.9%). All peptides selected in the last analysis present a high population coverage rate based on the interaction of HLA alleles (95.36 ± 7.83%). Therefore, the peptides characterized in this study are recommended for in vitro and in vivo studies and can provide the basis for the rational design of a vaccine against PA.

High levels of cAMP inhibit Pseudomonas aeruginosa biofilm formation through reduction of the c-di-GMP content

The human pathogen Pseudomonas aeruginosa can cause both acute infections and chronic biofilm-based infections. Expression of acute virulence factors is positively regulated by cAMP, whereas biofilm formation is positively regulated by c-di-GMP. We provide evidence that increased levels of cAMP, caused by either a lack of degradation or increased production, inhibit P. aeruginosa biofilm formation. cAMP-mediated inhibition of P. aeruginosa biofilm formation required Vfr, and involved a reduction of the level of c-di-GMP, as well as reduced production of biofilm matrix components. A mutant screen and characterization of defined knockout mutants suggested that a subset of c-di-GMP-degrading phosphodiesterases is involved in cAMP-Vfr-mediated biofilm inhibition in P. aeruginosa.

Bacterial toxins as immunomodulators

Bacterial toxins are the causative agent at pathology in a variety of diseases. Although not always the primary target of these toxins, many have been shown to have potent immunomodulatory effects, for example, inducing immune responses to co-administered antigens and suppressing activation of immune cells. These abilities of bacterial toxins can be harnessed and used in a therapeutic manner, such as in vaccination or the treatment of autoimmune diseases. Furthermore, the ability of toxins to gain entry to cells can be used in novel bacterial toxin based immuno-therapies in order to deliver antigens into MHC Class I processing pathways. Whether the immunomodulatory properties of these toxins arose in order to enhance bacterial survival within hosts, to aid spread within the population or is pure serendipity, it is interesting to think that these same toxins potentially hold the key to preventing or treating human disease.

Effect of Pseudomonas aeruginosa exotoxin A on IFN-gamma synthesis: expression of costimulatory molecules on monocytes and activity of NK cells

The aim of the study was (1) to evaluate the effect of Pseudomonas aeruginosa Exotoxin A (P-ExA) on the production of IFN-gamma in anti-CD3 induced human peripheral blood mononuclear cells (PBMC) and (2) to establish the effect of P-ExA on the IFN-gamma dependent cellular activities such as the expression of costimulatory molecules on monocytes and cytotoxicity of NK cells. The toxin in a high dose (100 ng/ml) inhibited IFN-gamma synthesis. Inhibitory effect of P-ExA was abolished by IL-1alpha which in a combination with P-ExA exerted a strong synergistic effect on IFN-gamma synthesis. Other monokines such as IL-1beta, IL-6, TNF-alpha neither reversed the inhibitory effect of P-ExA nor induced production of IFN-gamma. P-ExA also inhibited IFN-gamma-induced cellular events: (1) expression of costimulatory molecules on monocytes (CD80, CD86, ICAM-1, HLA-DR); (2) cytotoxic activity of NK cells. Inhibition of NK cells activity by P-ExA was not reversed by cytokines such as IL-2, IFN-alpha and TNF-alpha, which are known to enhance effector functions of NK cells. From these results we conclude that: (1) inhibition of IFN-gamma synthesis, as well as IFN-gamma-induced expression of costimulatory molecules and NK-cell effector functions may lead to suppression of specific and non-specific defense mechanisms, respectively, which are necessary for elimination of PA bacteria; (2) enhancement of IFN-gamma synthesis induced by P-ExA in a combination with IL-1alpha may cause harmful, Th1 cells dependent, inflammatory reactions of the host (septic shock, tissue damage) during infection with Pseudomonas aeruginosa.

GM-CSF is required for the Pseudomonas exotoxin A-induced proliferation of immature T cells in athymic mice

Previous studies have demonstrated that Pseudomonas exotoxin A stimulated the proliferation of immature T lymphocytes within the splenocytes of athymic mice. These studies were performed to determine which lymphokines were involved in the proliferation of the immature T cells. The results of this study indicate that exotoxin A does not induce the production of interleukin-2 or tumor necrosis factor from B cell-depleted splenotypes from athymic mice. However, exotoxin A does induce the production of granulocyte-macrophage colony-stimulating factor (GM-CSF) from B cell-depleted splenocytes. Furthermore, the GM-CSF was shown to be produced by a Thy1+, CD4-, CD8- T lymphocyte. The addition of anti-GM-CSF antibody abrogates the exotoxin A-induced proliferation of B cell-depleted splenocytes from athymic mice. Thus, these data indicate that exotoxin A induces the production of GM-CSF from immature T lymphocytes within the splenocytes of athymic mice and the exotoxin A-induced proliferation of these immature T cells is dependent on the presence of GM-CSF.

In vivo production of exotoxin A and its role in endogenous Pseudomonas aeruginosa septicemia in mice

We have examined the production of Pseudomonas aeruginosa exotoxin A (ETA) and its role in endogenous bacteremia in mice. Mice given P. aeruginosa D4 orally died of bacteremia between days 10 and 13 following cyclophosphamide-induced leukocytopenia. In this model, serum endotoxin was detected beginning on day 7 by the Limulus assay and P. aeruginosa was cultured from blood beginning on day 9. ETA and tumor necrosis factor alpha (TNF) were also detected in serum by enzyme-linked immunosorbent assay beginning on day 9. Purified ETA did not stimulate the production of TNF in normal mice primed with a synthetic derivative of muramyl dipeptide in the absence of endotoxin. However, ETA enhanced and primed endotoxin-induced TNF production in mice. The mortality rate of mice given ETA mutant PAO-PRI (5.0%) was significantly lower than that of mice given the parent strain (78.8%). These data indicate that ETA may be an important factor in the occurrence of P. aeruginosa bacteremia and/or the death of mice. Also, ETA may be responsible for enhancing the production of a lethal dose of TNF in the presence of endotoxin in P. aeruginosa bacteremia.

Murine interferon-gamma enhances resistance to infection with strains of Pseudomonas aeruginosa in mice

This study focused on the role of recombinant murine interferon-gamma (rMuIFN-gamma) in modulating resistance to infections produced by Pseudomonas aeruginosa in mice. CBA/C mice were treated with rMuIFN-gamma, exposed to thermal injury, and challenged with P. aeruginosa organisms. Survival of infected, burned mice was determined over a period of 14 days and compared with control animals not receiving rMuIFN-gamma. Two clinical isolates of P. aeruginosa that differed originally in the ability to produce metalloproteases, were used to infect the mice. When the mice were pretreated with rMuIFN-gamma before the infection, no statistically significant differences in survival were observed with either of the two strains of bacteria compared to controls. However, when mice were pretreated and injected therapeutically with rMuIFN-gamma (continued receipt of rMuIFN-gamma after infection), there was a significant protective effect in animals infected with one of the strains of P. aeruginosa. We conclude that rMuIFN-gamma may be useful in treating infections with certain strains of P. aeruginosa in mice.

Evidence for Kupffer cell activation by burn injury and Pseudomonas exotoxin A

Postburn metabolic and immunological alterations may in part be due to translocation of gut exotoxin and endotoxin, which can result in tumour necrosis factor (TNF) and prostaglandin E (PGE) production by macrophages. We evaluated the effect of burn injury, plus exotoxin and endotoxin on TNF-alpha and PGE production by Kupffer cells, and peritoneal macrophages. Adult Wistar rats underwent 30 per cent TBSA burn or sham burn. Kupffer cells were harvested from rat livers and peritoneal macrophages from the abdominal cavity 24 h postburn. They were cultured overnight at 1 x 10(6) cells/ml and stimulated with saline, 5 micrograms/ml of Pseud. aeruginosa Exotoxin A (Exo-A), 5 micrograms/ml of Pseud. aeruginosa Endotoxin (Endo), Exo-A + Endo, or Exo-A + Endo + the PGE derivative 16,16 dimethyl-PGE (dPGE) (10 micrograms/ml). The supernatants were harvested after 4, 24 and 48 h of culture and assayed for TNF-alpha and PGE. Results showed that burn injury induced an increase in TNF-alpha and PGE production by Kupffer cells stimulated with Exo-A, Endo, and both Exo-A + Endo (P < 0.05). The release of TNF-alpha by Kupffer cells was downregulated by exogenous PGE (P < 0.05). The increased TNF-alpha production was inversely related to PGE levels. In conclusion, both burn injury and Exo-A potentiate the responsiveness of Kupffer cells and peritoneal macrophages to endotoxin as measured by the rate of production of TNF-alpha and PGE. PGE may locally downregulate the immune response by limiting Kupffer cells' and peritoneal macrophages' TNF-alpha production.

Immunosuppressive effects of Pseudomonas aeruginosa exotoxin A on human B-lymphocytes

In this study we investigated the effects of exotoxin A on proliferation and differentiation of human B-cells in vitro. Exotoxin A at a concentration of 1 microgram/ml inhibited the proliferation of B-cells preactivated by insolubilized anti-IgM antibody or by formalinized Staphylococcus aureus particles, plus IL-2 or IL-4. B-cell blasts obtained after preactivation of tonsillar B-cells produce IgG and IgM in culture supernatants, and this Ig production is enhanced by IL-2 or IL-4. Exotoxin A inhibited the production of IgG and IgM by the B-blasts at the concentration of 1 microgram/ml.

Selective activation of murine V beta 8.2 bearing T cells by Pseudomonas exotoxin A

We have determined that Pseudomonas aeruginosa exotoxin A (PE) can selectively stimulate the proliferation of V beta bearing T lymphocytes. Murine thymocytes were fractionated by selective agglutination with peanut agglutinin (PNA) and the PNA- thymocytes, which represent mature thymocytes, were shown to be responsive to PE stimulation. In addition, mature peripheral T lymphocytes (nylon wool nonadherent splenocytes) were also observed to respond to PE stimulation. Both CD4+ and CD8+ splenic T lymphocyte populations proliferated in response to PE. Flow microfluorimetry analysis of PNA- thymocytes stimulated with PE indicated that V beta 8.2 bearing T cells were preferentially expanded. Thus, our data indicate that PE represents a microbial super antigen which stimulates murine thymocytes which bear the V beta 8.2 element of the T cell receptor.

Induction of tumor necrosis factor (TNF) and interleukin-1 (IL-1) by Pseudomonas aeruginosa and exotoxin A-induced suppression of lymphoproliferation and TNF, lymphotoxin, gamma interferon, and IL-1 production in human leukocytes

Pseudomonas aeruginosa is a dominant pathogen in infection in cystic fibrosis. This bacterium is thought to play a major role in the chronic bronchial infection-induced pathophysiology. Our data showed that whole formalin-fixed heat-killed P. aeruginosa was mitogenic for human lymphocytes and induced production of substantial amounts of tumor necrosis factor alpha (TNF) in peripheral blood mononuclear leukocytes in cultures. Significant amounts of TNF were produced at 10(3) bacteria per 2 x 10(5) mononuclear leukocytes. Treatment of P. aeruginosa with polymixin B did not affect its ability to stimulate TNF production, suggesting that bacterial lipopolysaccharide is not involved. P. aeruginosa, however, did not stimulate production of the T-cell lymphokine lymphotoxin (TNF beta). Exotoxin A, considered to be an important virulence factor produced by P. aeruginosa, did not stimulate either lymphoproliferation or production of TNF. In fact, this toxin, at nontoxic concentrations, was found to depress lymphoproliferation induced by phytohemagglutinin and Staphylococcus aureus and decreased production of TNF, lymphotoxin, and gamma interferon in either lymphocytes or macrophages. This toxin similarly inhibited the production of interleukin-1 beta (IL-1 beta) and IL-1 alpha, but for the inhibition of the latter, 25-fold-less toxin was required than for inhibition of the former. Inhibition of production of TNF was as sensitive as the IL-1 alpha to exotoxin A. The effects of exotoxin A on lymphoproliferation and cytokine production could be neutralized by the addition of anti-exotoxin A antibodies. These results suggest that two mechanisms by which P. aeruginosa could contribute to the chronic bronchial infection-induced pathophysiology are the nonspecific stimulation of TNF and IL-1 and the release of exotoxin A, a toxin which depresses immune responses.

Induction of interleukin-1 from murine peritoneal macrophages by Pseudomonas aeruginosa exotoxin A

Pseudomonas exotoxin A, an ADP-ribosylating toxin produced by Pseudomonas aeruginosa, has been shown to stimulate the proliferation of murine thymocytes, which requires the participation of accessory cells. This requirement for accessory cells can be replaced by supernatant from adherent peritoneal exudate cells that have been stimulated with exotoxin A. Antibody to exotoxin A inhibits the induction of the thymocyte mitogenic activity from adherent peritoneal macrophages. However, antibody to exotoxin A had no effect on the thymocyte proliferation if the antibody was added to supernatant which contained thymocyte mitogenic activity. The thymocyte mitogenic activity was associated with a protein or protein complex with a molecular mass of greater than 10,000 daltons. D10 bioassays indicated the presence of interleukin-1 (IL-1) in the supernatant. Antibody to IL-1 inhibited the ability of supernatant to induce thymocytes to proliferate. Therefore, these data suggest that Pseudomonas exotoxin A can stimulate the production of IL-1 from adherent peritoneal cells, which induces murine thymocytes to proliferate.

Induction of inflammatory mediators (histamine and leukotrienes) from rat peritoneal mast cells and human granulocytes by Pseudomonas aeruginosa strains from burn patients

Clinical isolates of Pseudomonas aeruginosa from severely burned patients were analyzed with regard to their capacity to induce inflammatory-mediator release from rat mast cells or human granulocytes. The bacterial strains were characterized according to their cell-associated hemolysin activity as well as their secreted hemolysin and phospholipase C activities. P. aeruginosa expressing heat-labile hemolysin and phospholipase C induced histamine release from rat mast cells and leukotriene formation from human granulocytes, while bacterial strains expressing heat-stable hemolysin were potent releasers of histamine but did not lead to leukotriene formation. The mediator-inducing capacity was dependent on the growth characteristics of the bacterial strains. The purified glycolipid (heat-stable hemolysin) of P. aeruginosa was a potent inducer of histamine release but did not initiate leukotriene formation. Exotoxin A did not affect inflammatory-mediator release. P. aeruginosa with leukotriene-inducing capacity also enhanced omega oxidation of endogenous leukotriene B4, suggesting an additional inactivation of the chemotactic potential. Our data suggest that both hemolysins of P. aeruginosa contribute to the pathogenicity of P. aeruginosa by inducing and modulating inflammatory-mediator release from various cells.

Inhibition of human lymphocyte proliferation and cleavage of interleukin-2 by Pseudomonas aeruginosa proteases

This study was undertaken to determine the effect of Pseudomonas aeruginosa alkaline protease (AP) and elastase (ELA) on human lymphocyte function. AP at 50 micrograms/ml and ELA at 12 micrograms/ml caused a 50% inhibition of phytohemagglutinin-induced proliferation. There was no difference in the effect of proteases on CD4- and CD8-positive cells. To determine the effect of proteases on interleukin-2 (IL-2)-induced cell proliferation, the proteases and IL-2 were added to the IL-2-dependent CTLL-2 cell line. AP and ELA inhibited the proliferation of these cells. When IL-2 was added in excess, the inhibition was partly reversed. ELA at 10 micrograms/ml cleaved IL-2, as judged by size chromatography of a reaction mixture containing 125I-labeled IL-2 and the proteases. The ELA-digested IL-2 exhibited a reduced binding capacity to IL-2 receptors on the lymphocytes. Furthermore, treatment of phytohemagglutinin-stimulated lymphocytes with AP and ELA resulted in inhibition of binding of intact IL-2 to IL-2 receptors on the stimulated lymphocytes. These results indicated that P. aeruginosa-derived enzymes are able to interfere with human lymphocyte function in vitro and that this effect might be due to cleavage of IL-2.

Biological effects of Pseudomonas aeruginosa exotoxin A: lymphoproliferation of T lymphocytes in athymic mice

Pseudomonas aeruginosa exotoxin A has been observed to exert modulatory effects on the immune response. The present study examines the ability of exotoxin A to induce proliferation of splenocytes from athymic nu/nu mice. We observed that exotoxin A induced the proliferation of athymic nude splenocytes which could be abrogated by heating the toxin at 70 degrees C or by preincubation of the toxin with rabbit anti-exotoxin A antiserum. Photoaffinity-labelled toxin significantly induced splenocyte proliferation although the relative activity was reduced. Maximum nude splenocyte proliferation was observed at a toxin dose of 100 ng. This same dose was shown previously for athymic splenocytes to induce an enhanced response to the thymus-dependent (TD) antigen, sheep red blood cells (SRBC). The increased [3H]-TdR uptake in athymic splenocytes stimulated by exotoxin A was initiated by 24 hours and continued to day 10. Nude splenocytes depleted of Ig+ and Ia+ cells were induced to proliferate by exotoxin A. Cyclosporin A addition abrogated the ability of exotoxin A to induce proliferation. These results suggest that Pseudomonas aeruginosa exotoxin A can stimulate the proliferation of splenic T lymphocytes in athymic nu/nu mice.

Immunomodulation and Chlamydia: immunosuppression and the protective immune response to C. psittaci in mice

Mice immunized intramuscularly with a low dose, viable inoculum of C. psittaci survived an otherwise lethal intraperitoneal challenge with the homologous chlamydial strain. Immunized animals were not protected from intraperitoneal challenge by the unrelated pathogen, Listeria monocytogenes. Spleen cells from animals that exhibited protective immunity were suppressed in their proliferative responses to mitogens or chlamydial antigen in an in vitro blastogenic assay. This suppression was transferable to normal spleen cells by adding irradiated cells from immunized animals to normal cell populations. The degree of normal cell blastogenic suppression was dependent on the ratio of irradiated immune to normal cells present in the assay medium. Suppression of humoral responses was demonstrated in vivo. Immunized animals were incapable of producing antibody secreting cells to sheep red blood cells after an intraperitoneal inoculation of SRBC. Unimmunized animals produced a significant number of plaque forming cells as measured by a direct plaque forming cell assay. Lymphokine activity was not impaired in spleen cells from mice that exhibited other manifestations of suppression. Taken together, these data provide evidence to indicate that the induction of suppression may not correlate with increased pathogenesis, but rather be closely associated with protective immunity. Data also provide circumstantial evidence to indicate that lymphokine induction may be important in the development of protective immunity to C. psittaci in the mouse.

Induction of murine cytolytic T lymphocytes by Pseudomonas aeruginosa exotoxin A

Pseudomonas aeruginosa exotoxin A (PA), a potent protein synthesis inhibitor, was found to be a weak T-cell mitogen for murine splenocytes. Maximal stimulation of [3H]thymidine incorporation was obtained with 10 to 100 ng of toxin per ml following a 4-day induction. PA was also shown to be a polyclonal activator of cytolytic T lymphocytes (CTL), effective against concanavalin A-treated target cells. The effective PA dose for CTL induction was the same as that for mitogenic stimulation, only with a prolonged priming time (7 days). In contrast to other mitogens, PA could not reactivate memory CTL into secondary CTL. The stimulation of CTL by subcytotoxic doses of PA may be relevant to its modulatory effect on the immunocellular system.

Suppression of the cytotoxic T-lymphocyte response in mice by pertussis toxin

Pertussis toxin (PT), the major toxin produced by Bordetella pertussis, has been reported both to enhance and to suppress immune responsiveness. These findings suggested that PT contributes to the virulence of B. pertussis through mechanisms involving immune regulation. We report that PT suppressed both the primary and the secondary cytotoxic T-lymphocyte (CTL) responses of mouse spleen cells cultured against two different allogeneic stimulator spleen cells in vitro. This suppression was dependent on the dose of PT used. PT must be present during the initial stages (within the first 24 hr) of CTL generation. Soluble factor(s) obtained from spleen cells preexposed to PT did not suppress the CTL response. Suppression of the CTL response observed was not due to depletion of the antigen by PT. The cytotoxic activity of CTL clones could not be suppressed by PT. The analysis of responder spleen cells, fractionated by anti-immunoglobulin panning techniques, provided evidence that L3T4-, Lyt 2+ cells mediate the PT-induced immunosuppression. We propose that suppression of the CTL response by PT is generated through the activation of L3T4-, Lyt 2+ suppressor T lymphocytes.

Suppression of the delayed-type hypersensitivity and cell-mediated immune responses to Listeria monocytogenes induced by Pseudomonas aeruginosa

Pseudomonas aeruginosa-mediated suppression of the immune response to Listeria monocytogenes was investigated in mice. Because delayed-type hypersensitivity (DTH) footpad swelling to L. monocytogenes was suppressed equally in lipopolysaccharide-responsive and -hyporesponsive mouse strains, the lipopolysaccharide component of P. aeruginosa could not have been the suppressive agent. Mucoid P. aeruginosa cells were no more suppressive than their nonmucoid revertants; therefore, mucoid coating was not an additional immunosuppressive element. Interleukin-1 and macrophage inhibitory factor production to L. monocytogenes and clearance of L. monocytogenes from mouse spleens were all decreased by prior Pseudomonas infection, indicating that cell-mediated immunity, as well as DTH, was decreased to a sublethal Listeria dose. The timing of Pseudomonas exposure relative to Listeria sensitization was varied. P. aeruginosa injected 24 or 6 h before or at the same time as L. monocytogenes depressed DTH to Listeria challenge 7 days later. Animals treated in this way could not respond to reinfection with L. monocytogenes at 13 days. P. aeruginosa administered to L. monocytogenes-sensitized mice at the time of footpad challenge was suppressive, but these mice responded normally upon reinfection. It appears that P. aeruginosa induced two types of suppression to L. monocytogenes: a transient suppression, affecting DTH challenge but not resensitization, and a longer lasting suppression that did not permit mice exposed to P. aeruginosa at the time of Listeria sensitization to respond to subsequent Listeria exposure.

Variables which affect suppression of the immune response induced by Pseudomonas aeruginosa exotoxin A

Pseudomonas exotoxin A has been shown previously to induce suppression of the murine immune response. In the present study, various parameters were examined which may have an effect on immunosuppression. The addition of 10(-4) ng of exotoxin A induced suppression of the immune response to trinitrophenylated Ficoll from days 3 to 10, while 10 ng of toxin exerted no suppressive effect over the same examination periods. When the toxin was administered 1 or 2 days before antigen stimulation, suppression of the response was observed with both 10 and 10(-4) ng. Priming splenocytes with toxin either in vivo or in vitro for 1 or 2 days suppressed the response of fresh cultured splenocytes to antigenic stimulation. Heated toxin, photoaffinity-labeled toxin, or preincubation of the toxin with rabbit anti-exotoxin A antiserum eliminated the toxin-induced suppression. These results suggest that Pseudomonas exotoxin A can generate multiple biological effects.

Induction of an immune response in athymic nude mice to thymus-dependent antigens by Pseudomonas aeruginosa exotoxin A

Exposure of spleen cells from athymic nude mice to Pseudomonas aeruginosa exotoxin A induces these cells to respond to the thymus-dependent (TD) antigen sheep erythrocytes (SRBC). The response induced by toxin is dose dependent, antigen specific, and not due to polyclonal B-cell activation. Enhancement of the anti-SRBC response can be observed when toxin addition precedes antigen stimulation by 24-48 hr, which decreases when toxin administration follows antigen stimulation. A significant response is also observed when toxin and antigen are added simultaneously. A significant anti-SRBC response can be observed out to Day 10 postantigen and toxin stimulation after attaining a peak response at Day 5. Cultures exposed to toxin in the presence or absence of antigen exhibited a higher cell number and relative number of B cells as compared to control cultures. Exposure of T-cell depleted B cells from euthymic +/nu mice to toxin plus antigen does not result in an anti-SRBC response indicating that exotoxin A alone is not sufficient to induce B-cell responsiveness to T-dependent antigens and that other cells and/or factors are involved in the toxin-induced responsiveness of nude mice to T-dependent antigens.

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.