Immunological responses of L. donovani infection in mice and significance of T cell in resistance to experimental leishmaniasis.

The parasite burdens of livers and spleens of several strains of mice following infection with L. donovani were determined for a period of over 120 days. The parasite loads of the spleens and livers were correlated with the development of immunity to reinfection, footpad sensitivity and antibody titres. The strains of mice studied could be divided into two groups--those highly susceptible and those relatively non-susceptible. The antibody in the susceptible strains appeared 12 days after infection and increased thereafter. The antibody in the less susceptible strains appeared some time later and remained at the same level throughout the test period. In strains CAFl, C57B1/6 and BALB/c skin reactivity to Leishmania antigen developed at the time when the parasite burden had decreased from its peak. Skin reactivity never developed in DBA!l mice, the most highly susceptible strain, and in A/j the least susceptible strain. The development of resistance to reinfection with L. donovani following i.v. and i.p. infection was observed in C57Bl mice. Upon cell transfer from these immune animals, it was found that protective immunity was mediated through the thymus-dependent lymphocytes. Serum from immune mice was not able to confer immunity to the recipient animals.