Examination of the differential characteristics of amplifier and contrasuppressor T cells

Effect of adjuvant composition on immune response to a multiple antigen peptide (MAP) containing a protective epitope from Neisseria meningitidis class 1 porin

A variety of adjuvants with the potential for use with experimental human vaccines were used for immunisation of mice, in an attempt to augment the humoral immune response to a multiple antigen peptide (MAP) containing a protective epitope from the sero-subtype specific class 1 porin protein of Neisseria meningitidis, in tandem with a Th-cell epitope. Surface plasmon resonance showed that combinations of the immunomodulators pluronic block co-polymer, muramyl dipeptide and monophosphoryl lipid A (MPL), increased the magnitude and avidity of the immune response in comparison with both Al(OH)3 and Freund-type adjuvants. In addition, the incorporation of MPL was essential for the induction of a broad distribution of antibody isotypes. The antibodies induced recognised the native protein in meningococcal outer membranes in a subtype-specific manner. The formulations containing these multiple immunomodulators which have already been used in human phase I/II trials with experimental vaccines, are candidates for inclusion in future human vaccines based on synthetic peptides containing defined, protective epitopes.

The glucuronoxylomannan of Cryptococcus neoformans serotype A is a type 2 T-cell-independent antigen

The humoral immune response of inbred mice to immunization with the glucuronoxylomannan (GXM) of Cryptococcus neoformans was investigated both serologically and in plaque-forming cells (PFCs). The T-helper-cell-independent quality of the GXM was demonstrated by using BALB/c nu/nu mice. Primary and secondary dose responses to three antigenic forms of GXM, (i) the native antigen, (ii) a GXM-bovine serum albumin protein conjugate, and (iii) a cryptococcal whole-cell vaccine, revealed a lack of isotype class switching and anamnestic responses. Both the levels of complement-fixing anti-GXM antibody in serum and the PFC responses in the athymic mice showed no significant differences from those in the wild-type controls. However, T cells are involved in the suppression of the primary response to GXM. When BALB/cBy mice were given rabbit anti-mouse thymocyte serum along with 0.5 microgram of GXM, both antibody levels in serum and PFC responses were significantly increased over those of control mice that received GXM and normal rabbit serum. In addition, T cells were also shown to enhance the primary immune response to GXM. BALB/cBy mice were given GXM and anti-mouse thymocyte serum on day 1. On day 2, the experimental group was given anti-mouse thymocyte serum and the control group was given saline. On day 5, comparison of the PFC responses and anti-GXM antibody titers of the two groups revealed a significant increase in the immune response of the control over the experimental group. The type 2 T-cell-independent quality of GXM was also demonstrated in CBA/cHN xid mice. These mice lack the Lyb+ subset of B cells and are unable to respond to type 2 T-independent antigens but respond normally to type 1 T-independent antigens. Type III pneumococcal polysaccharide, a type 2 T-independent antigen, was used as a negative control, and trinitrophenyl-lipopolysaccharide, a type 1 T-independent antigen, was used as a positive control. The CBA/cHN xid mice failed to respond to either type III pneumococcal polysaccharide or GXM but did not respond to immunization with trinitrophenyl-lipopolysaccharide. BALB/cBy mice responded normally to all three antigens.

Differential sensitivity of CD8+ suppressor and cytotoxic T lymphocyte activity to bacterial monophosphoryl lipid A

Treatment with a preparation of monophosphoryl lipid A, known to be capable of abolishing the expression of CD8+ suppressor T cell activity generated during the antibody response to type III pneumococcal polysaccharide (SSS-III), was found to have no adverse effect upon either induction or expression of CD8+ cytotoxic T lymphocyte activity specific for influenza A virus antigens. This suggests that suppressor T cells and cytotoxic T lymphocytes represent functionally distinct subsets of CD8+ T cells which can be differentiated on the basis of their sensitivities to inactivation by monophosphoryl lipid A.

Inactivation of suppressor T cell activity by the nontoxic lipopolysaccharide of Rhodopseudomonas sphaeroides

Antibody responses of mice immunized with type III pneumococcal polysaccharide were examined with and without treatment with nontoxic lipopolysaccharide from Rhodopseudomonas sphaeroides (Rs-LPS). The results obtained were similar to those described previously for mice treated with monophosphoryl lipid A (MPL) except that lower amounts of Rs-LPS were needed. Both were without effect when given at the time of immunization with type III pneumococcal polysaccharide but elicited significant enhancement when given 2 to 3 days later. Such enhancement was T cell dependent and not due to polyclonal activation of immunoglobulin M synthesis by B cells. Treatment with either Rs-LPS or MPL abolished the expression but not induction of low-dose paralysis, a form of immunological unresponsiveness known to be mediated by suppressor T cells (Ts). The in vitro treatment of cell suspensions containing Ts with extremely small amounts of Rs-LPS or MPI completely eliminated the capacity of such cells to transfer suppression to other mice. These findings indicate that the immunomodulatory effects of both MPL and Rs-LPS are mainly the result of eliminating the inhibitors effects of Ts; this permits the positive effects of amplifier T cells to be more fully expressed, thereby resulting in an increased antibody response. The significance of these and other findings to the use of Rs-LPS as a pharmacotherapeutic agent for gram-negative bacterial sepsis is discussed.

Enrichment of suppressor T cells by means of binding to monophosphoryl lipid A

The binding and elution of spleen cells from plastic dishes coated with monophosphoryl lipid A (MPL) resulted in a greater than 1,000-fold enrichment of antigen-specific suppressor T-cell (TS) activity when spleen cells from mice 18 to 24 h after exposure to a low dose of type III pneumonococcal polysaccharide (SSS-III) were used. The removal of MPL-adherent TS cells resulted in an increase in the degree of amplifier T-cell (TA) activity present in the remaining MPL-nonadherent cell fraction; however, both TS and TA activities were found in the MPL-adherent cell fraction when spleen cells from mice 4 days after immunization with an optimal dose of SSS-III were examined. These findings, as well as others, suggest that both TS and TA, once activated, acquire a cell surface receptor that enables them to bind to MPL. Because of differences in the kinetics for the activation of TS and TA during the course of the antibody response and the fact that TS, but not TA, activity appears as early as 18 to 24 h after exposure to SSS-III, it is possible to use this experimental approach to obtain cell suspensions greatly enriched in TS activity.