Interactions between Mycobacterium leprae and simian immunodeficiency virus (SIV) in rhesus monkeys

Groups of rhesus monkeys were inoculated with: 1) simian immunodeficiency v irus (SIV)(B670) alone; 2) Mycobacterium leprae alone; 3) SIV plus M. lepra e on the same day; and 4) M. leprae 2 weeks after SIV. Animals were monitor ed at intervals for virus loads, antibody responses to M. leprae glycolipid antigens and to SIV Gp120, T-cell CD4 + anti CD4 + CD29 + subset percentag es, leprosy and acquired immunodeficiency syndrome (AIDS) clinical symptoms . Five out of six animals developed leprosy in each co-inoculated group, co mpared to one out of six in the M. leprae-only-inoculated group, indicating that M. leprae/SIV co-infection increases the susceptibility to leprosy, r egardless of the timing of the two infections. Animals in the co-infected g roup that received M. leprae 2 weeks after SIV had a significantly slower r ate of AIDS progression and long-term survival was significantly greater (t hree out of six) compared to the group inoculated with SIV alone I:zero out of seven). All M. leprae-only-inoculated animals (six out of six) survived . Post-SIV-inoculation, a rapid decrease in the percentages of CD4 + and CD 4 + CD29 + T-cells was observed in the SIV-only-inoculated group that was s ignificantly blocked by co-inoculation with M. leprae 2 weeks after SIV, bu t not by SIV on the same day. The virus load set point was increased by app roximately two logs in the group inoculated with M. leprae and SIV on the s ame day compared to SIV 2 weeks prior to M. leprae or the SIV-only-inoculat ed group. The results indicate that M. leprae, inoculated 2 weeks after SIV , decreased the pathogenicity of SIV compared to inoculation of M. leprae a nd SIV on the same day or SIV alone. The decreased pathogenicity correlated with a diminished loss of CD4 + and CD4 + CD29 + T-cell subsets in the gro up inoculated with M. leprae 2 weeks after SIV compared to the group inocul ated with SIV alone. IgG antibody responses to M. leprae-specific cell wall phenolic glycolipid-I antigen were inhibited by 2-week-prior or same-day S IV co-inoculation compared to M.:leprae-only inoculated animals. The IgG an ti-lipoarabinomannan antibody response was enhanced in the group inoculated with M. leprae and SIV on the same day compared to the groups inoculated w ith M. leprae alone or SIV 2 weeks prior to M. leprae. Antibody responses t o SIV Gp120 antigen were unimpaired in both co-inoculated groups compared t o SIV-only-inoculated groups. The antibody results show that the immune res ponses to SIV and M. leprae are interrelated in SIV/M. leprae co-infected a nimals.