Modulation of murine Peyer's patch immunoglobulin A response by enterotoxigenic Escherichia coli.

Enterotoxigenic Escherichia coli (ETEC) may have profound effects on the capacity of gut-associated lymphoid tissue to mount a secretory immune response because of the potential ability of heat-stable toxin or heat-labile toxin to modulate the immune response. To examine the effects of ETEC or its purified enterotoxins upon the humoral immune response of murine small intestinal Peyer's patch lymphocytes, BDF1 (lipopolysaccharide-responder) and C3H/HeJ (lipopolysaccharide-nonresponder) mice were orally primed with sheep erythrocytes (SRBC) four times during a 2-week period to initiate differentiation of Peyer's patch B lymphocytes to cells committed to anti-SRBC immunoglobulin A (IgA) production. Halfway through the oral priming regimen the mice were gastrically intubated with 10(8) ETEC, 10(8) non-ETEC, or saline. ETEC persisted in the small intestine for at least 7 days at a level of 10(3) to 10(4) bacteria per mouse. Seven days after the last oral dosing with SRBC, Peyer's patch lymphocytes were removed from infected or saline-treated mice and incubated in vitro with SRBC. The ETEC infection had a small effect on the anti-SRBC IgM plaque-forming cell response of SRBC-primed mice but inhibited significantly the anti-SRBC IgA plaque-forming cell response in both BDF1 and C3H/HeJ mice as compared with uninfected controls. The non-ETEC, an isolate from normal mouse small intestine, had no significant effect on either IgM or IgA anti-SRBC plaque-forming cell response. Purified heat-labile toxin, not heat-stable toxin, alone in a dose-dependent manner significantly inhibited both the IgA and IgM plaque-forming cell response of Peyer's patch lymphocytes from primed mice. These data suggest that ETEC can inhibit the development of the gut-associated lymphoid tissue IgA immune response through the immunopharmacological effect of an enterotoxin, the heat-labile toxin.

Differential effects of nordihydroguaiaretic acid (NDGA) on B-cell subsets: reversal of NDGA-induced antibody suppression by cyclic GMP is subset specific.

Nordihydroguaiaretic acid (4,4'-[2,3-dimethyl tetramethylene]-dipyrpcatechol) (NDGA), a reportedly specific lipoxygenase inhibitor, suppressed the in vitro murine plaque-forming cell (PFC) response to a thymus-dependent (TD) antigen, and the two subclasses of thymus-independent (TI) antigens, TI1 and TI2, at a final concentration of 33 microM. Suppression kinetics were inconsistent with those observed in previous experiments for other lipoxygenase inhibitors, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), in that BHA and BHT exert suppression early in the 5-day PFC culture system, whereas NDGA suppressed through the 96th h of the 120 h culture period. The sulfhydryl-protective agent 2-mercaptoethanol (2ME) protected both the TD and TI responses. Dibutyryl cyclic GMP (dbcGMP) failed to restore NDGA-suppressed TD and TI1 PFC responses but restored the TI2 response when added at 0-, 24-, 48-, 72-, and 96-h at concentrations of 1-2 mM. NDGA inhibited lipopolysaccharide- (LPS-) induced increases in murine splenocyte cyclic GMP (cGMP) levels, and dbcGMP failed to accelerate the onset of the TI2 PFC response appreciably. The results of these and other laboratory studies indicated that NDGA may not be a specific inhibitor of lipoxygenase. Furthermore, the B-cell subset responding to TI2 antigens may be separated from the TD- and TI1-responding subsets because of the ability of dbcGMP to restore NDGA-suppressed TI2 responses but not the TD or TI1 response. The results suggest a fundamental difference in the biochemical pathways of B-cell subsets, and that cGMP metabolism in some cells may be linked to specific protein synthesis.

Disparate in vivo and in vitro immunomodulatory activities of rhodamine B.

At nontoxic concentrations (1-10 microgram/ml) rhodamine B (N-[9-(2-carboxyphenyl)-6-(diethylamino)-3H-xanthen-3-ylidene]-N- ethylethanaminium chloride; D & C Red No. 19; CAS no. 81-88-9), a low-molecular-weight dye, suppressed the primary in vitro plaque-forming-cell response of BDF1 mouse spleen cells both to the thymus-dependent antigen, sheep red blood cells and to the thymus-independent antigen, E. coli 0127: B8 lipopolysaccharide. Suppression was effective when the D & C Red No. 19 was added at any time up to 48 hr of culture. Rhodamine B at concentrations from 1 to 10 microgram/ml significantly suppressed mitogen-induced proliferation of both B- and T-lymphocytes in vitro. BDF1 mice exposed to 50 and 100 ppm dye in their drinking water for 14 days prior to splenectomy gave a depressed in vitro plaque-forming-cell response to sheep red blood cells. In contrast, a significant enhancement of antibody response resulted when mice were exposed to the dye and sheep-red-blood-cell antigen was administered in vivo. Mitogen-induced B- and T-lymphocyte proliferation was also enhanced in mice exposed to the dye for 14 days.

Restoration by cyclic guanosine monophosphate and extracellular calcium of butylated hydroxyanisole-suppressed primary murine thymus-dependent antibody response.

The effect of dibutyryl cyclic guanosine monophosphate (dbc-GMP) on butylated hydroxyanisole (BHA)-induced suppression of the primary in vitro thymus-dependent antibody response of BDF1 mouse spleen cultures was studied. When added at 0 hr relative to antigen addition, 1 mg of dbc-GMP (8 mM) restored by greater than 70% the BHA-inhibited primary immunoglobulin (Ig)M plaque-forming cell (PFC) response to sheep erythrocytes (SRBC). The suppression was not reversed by the addition of 50 microgram of dibutryl cyclic adenosine monophosphate (dbc-AMP), which is known to reverse suppressor T-cell activity. The addition of 10 mM extracellular calcium (Ca2+) at the same time as antigen to BHA-inhibited cultures resulted in more than 80% restoration of the anti-SRBC PFC response. Quantitation of c-GMP by radioimmunoassay demonstrated that BHA lowered by 58% the c-GMP content of splenic lymphocytes and abrogated the ability of lipopolysaccharide of E. coli (LPS) to elevate c-GMP levels in splenic lymphocytes. The data suggest that BHA exerts its immunosuppressive effect on the primary in vitro antibody response by inhibiting guanylate cyclase activity and effectively lowering c-GMP levels; exogenous dbc-GMP and Ca2+ can freely reverse the immunosuppressive effect of BHA.

Inverse relationship between immune interferon induction and mitogen effects on the maturation of the primary antibody response.

Staphylococcal enterotoxin A (SEA) is both a potent inducer of immune interferon (IFN-gamma) and suppressor of the murine primary in vitro plaque-forming cell (PFC) response to the thymus-dependent antigen sheep erythrocytes (SRBC). Staphylococcal enterotoxin D (SED), which is structurally related to but antigenically different from SEA, is, in contrast, a poor inducer of IFN-gamma but a potent accelerator of PFC response maturation. SED added to cultures from 0.01 to 1.0 microgram/ml induced profound enhancement of the PFC response on day 3 of culture. SEA caused no acceleration of PFC maturation and suppressed the day 5 PFC response over an equivalent dose range. At the same concentration, SED only poorly induced IFN-gamma, while SEA was a potent IFN-gamma inducer. SED induced DNA synthesis in C57Bl/6 spleen cell cultures but not athymic nude (Nu/Nu) spleen cells, suggesting that SED is a T-cell mitogen. SED was most effective in accelerating PFC maturation and increasing the magnitude of the PFC response when added to cultures at the time of SRBC addition. SED was an equally effective adjuvant for SRBC of both high and low immunogenicity. Thus, two mitogens that are structurally related have diametrically opposite effects on the primary in vitro thymus-dependent antibody response that maybe related to their relative abilities to induce IFN-gamma. These effects could be related to differential activation of T-cell subpopulations.