Amplifier T cell activity is decreased in MRL/1 mice: failure of concanavalin A and anti-lymphocyte serum to enhance antibody responses to thymus-independent antigens.

In order to indirectly assess T and B cell function in vivo in spontaneously autoimmune MRL mice, IgM plaque forming cell (PFC) responses to the thymus-independent antigens type III pneumococcal polysaccharide (S3) and polyvinylpyrrolidone (PVP) were determined. Both MRL/Mp-lpr/lpr (MRL/l) and MRL/Mp+/+ (MRL/n) mice responded well to S3 and, in fact, low doses of S3 which are not immunogenic in normal strains of mice elicited good responses in MRL mice. PVP was less immunogenic than S3, however, doses of PVP which are considered sub-immunogenic in normal mice did elicit responses in MRL mice. The effect of ageing on S3 and PVP responsiveness in MRL mice was also determined. Responses to S3 and PVP declined minimally in MRL/l mice and were unchanged in MRL/n mice. Amplifier T cell (TA) activity in MRL mice was indirectly assessed by determining the effect on concanavalin A or anti-lymphocyte serum on PFC responses to S3 and PVP. Whereas significant enhancement of the S3 and PVP IgM PFC responses occurred in MRL/n mice, neither method elicited remarkable enhancement in MRL/l mice. The lack of IgM enhancement was not due to altered kinetics of activation nor to a switch to IgG PFC responses. Possible reasons for the apparent dysfunction of TA in MRL/l mice are discussed.