Lack of general immunosuppression during visceral Leishmania tropica infection in BALB/c mice: augmented antibody response to thymus-independent antigens and polyclonal activation.

Leishmania tropica causes a lethal visceral disease in highly susceptible BALB/c mice, with many immunopathologic features resembling those in human kala-azar. The responses to thymus-independent antigens of Type 1 and 2 (TI-1, TI-2) were compared in infected mice of susceptible BALB/c and resistant C57BL/6 strains at various times after infection. The infected BALB/c mice had an augmented response to both types of antigens at 45 days after infection. Later (day 76), the response to trinitrophenylated lipopolysaccharide (TNP-LPS, a TI-1 antigen) was diminished but that to dinitrophenylated Ficoll (DNP-Ficoll, a TI-2 antigen) remained statistically above the response of uninfected mice. The response of the resistant strain to either antigen was not modified as a result of the infection. Both strains showed significant polyclonal activation, which was considerably greater in the BALB/c than in the C57BL/6 mice. The observations presented here are in contrast to the widely held belief that a generalized nonspecific immunosuppression occurs in L. tropica infected BALB/c mice.