Increased activation of antigen-primed or memory B cells by bacterial lipopolysaccharide

Cytokines as adjuvants for vaccines: antigen-specific responses differ from polyclonal responses

The use of cytokines in the administration of vaccines has a unique value in obtaining the appropriate immune response and in ensuring a protective outcome. Earlier studies indicating that cytokines can influence the generation of a particular antibody isotype may represent an oversimplification of a more complex problem. Several studies discussed in this review show that the effect of a given cytokine on the immune response depends on whether one examines the antigen-specific response or the polyclonal response (i.e., total serum immunoglobulins). Further, a balanced regulation of immune responsiveness is important in maintaining homeostasis of the immune system. Consequently, for any vaccine that uses cytokines to boost the response, due consideration must be given to these important variables.

Immunosuppressive effects induced by the polysaccharide moiety of some bacterial lipopolysaccharides

The immunomodulatory properties of several lipopolysaccharides (LPS) derived from clinical isolates of Pseudomonas aeruginosa, Branhamella catarrhalis, and Bordetella pertussis were evaluated for their capacity to influence the magnitude of the antibody response to type III pneumococcal polysaccharide (SSS-III), which is known to be regulated by suppressor and amplifier T cells (Ts and Ta, respectively). The administration of LPS, two days after immunization resulted in a significant increase in the antibody response. Such enhancement may be due mainly to the ability of the lipid A moiety of LPS to abolish the negative effects of activated Ts, thereby enabling Ta function to be more fully expressed; however, B cell mitogenicity of the LPS molecule also may be involved. By contrast, treatment with LPS at the time of immunization with SSS-III induces significant suppression of the SSS-III-specific antibody response; such suppression is not induced by LPS or lipid A derived from Escherichia coli and Salmonella minnesota, and is independent of the capacity of LPS to activate B cells polyclonally, an activity generally attributed to the lipid A fraction of LPS. Studies conducted with the LPS of P. aeruginosa indicated that the suppression induced is T cell dependent and mediated by the polysaccharide (PS) fraction of LPS; it appears to be due-at least in part-to the capacity of PS to expand or increase the size of the precursor pool of Ts, activated in response to SSS-III. The significance of these findings to the pathogenesis of certain gram-negative infections is discussed.

Studies on B-cell memory. IV. Effects of lipopolysaccharide on primary and secondary antibody responses to T-independent type-2 (TI-2) antigen in mice

Effects of LPS on primary and secondary antibody responses to typical TI-2 antigens were investigated in mice. Simultaneous injection of LPS with a TI-2 antigen showed only little adjuvant effect on the following primary antibody response to the antigen. In contrast, either a single or multiple injections of LPS, prior to the immunization with a TI-2 antigen, significantly augmented the following primary antibody response to the antigen. LPS, however, inhibited the development of B-cell memory to a TI-2 antigen when administered together with the antigen. Moreover, an injection of LPS in mice, which had strong IgM and IgG B-cell memories to a TI-2 antigen, caused disappearance or profound reduction of the memories. The results suggest that LPS produced by gram-negative bacteria exerts inhibitory effects on the development and continuation of B-cell memory to bacterial infections.

Adjuvant effects of trehalose dimycolate on the antibody response to type III pneumococcal polysaccharide

Treatment with trehalose dimycolate (TDM) increases the magnitude of the immunoglobulin M (IgM) antibody response of mice to type III pneumococcal polysaccharide (SSS-III). Such enhancement is demonstrable over a wide range of immunizing doses and does not require thymus-derived (T) cells to be elicited. Although young adult mice immunized with SSS-III do not usually make anti-SSS-III antibodies of the IgG1 and IgG3 classes, antibodies of one or both isotypes were produced after immunization and treatment with TDM and/or monophosphoryl lipid A (MPL); the additive nature of the effect produced by both TDM and MPL suggests that the two immunomodulators act by different mechanisms. TDM and MPL have different effects on the induction and expression of low-dose immunological paralysis, a form of unresponsiveness known to be mediated by suppressor T cells. The relevance of these findings to the modes of action of TDM and MPL is discussed.

Inactivation of suppressor T-cell activity by nontoxic monophosphoryl lipid A

Treatment with nontoxic monophosphoryl lipid A (MPL), which was derived from a polysaccharide-deficient, heptoseless Re mutant of Salmonella typhimurium, was found to inactivate suppressor T-cell activity, as evidenced by a decrease in the degree of low-dose immunological paralysis expressed and an increase in the magnitude of the antibody response to type III pneumococcal polysaccharide. The effects produced, which could not be attributed to the polyclonal activation of immune B cells by MPL, were dependent upon the dose of MPL used, as well as the time when MPL was given relative to low-dose priming or immunization with type III pneumococcal polysaccharide. Neither amplifier nor helper T-cell activity was decreased by treatment with the same, or larger, doses of MPL. The significance of these findings to the use of MPL as an immunological adjuvant or an immunomodulating agent is discussed.