Direct inoculation of simian immunodeficiency virus from sooty mangabeys in black mangabeys (Lophocebus aterrimus): first evidence of AIDS in a heterologous African species and different pathologic outcomes of experimental infection.

A unique opportunity for the study of the role of serial passage and cross-species transmission was offered by a series of experiments carried out at the Tulane National Primate Research Center in 1990. To develop an animal model for leprosy, three black mangabeys (BkMs) (Lophocebus aterrimus) were inoculated with lepromatous tissue that had been serially passaged in four sooty mangabeys (SMs) (Cercocebus atys). All three BkMs became infected with simian immunodeficiency virus from SMs (SIVsm) by day 30 postinoculation (p.i.) with lepromatous tissue. One (BkMG140) died 2 years p.i. from causes unrelated to SIV, one (BkMG139) survived for 10 years, whereas the third (BkMG138) was euthanized with AIDS after 5 years. Histopathology revealed a high number of giant cells in tissues from BkMG138, but no SIV-related lesions were found in the remaining two BkMs. Four-color immunofluorescence revealed high levels of SIVsm associated with both giant cells and T lymphocytes in BkMG138 and no detectable SIV in the remaining two. Serum viral load (VL) showed a significant increase (>1 log) during the late stage of the disease in BkMG138, as opposed to a continuous decline in VL in the remaining two BkMs. With the progression to AIDS, neopterin levels increased in BkMG138. This study took on new significance when phylogenetic analysis unexpectedly showed that all four serially inoculated SMs were infected with different SIVsm lineages prior to the beginning of the experiment. Furthermore, the strain infecting the BkMs originated from the last SM in the series. Therefore, the virus infecting BkMs has not been serially passaged. In conclusion, we present the first compelling evidence that direct cross-species transmission of SIV may induce AIDS in heterologous African nonhuman primate (NHP) species. The results showed that cross-species-transmitted SIVsm was well controlled in two of three BkMs for 2 and 10 years, respectively. Finally, this case of AIDS in an African monkey suggests that the dogma of SIV nonpathogenicity in African NHP hosts should be reconsidered.

Lessons learnt from studies of the immune characterization of naturally SIV infected sooty mangabeys.

The vast number of African non-human primates species that are naturally infected with the simian immunodeficiency viruses ( SIV) but have not shown any signs of lentivirus associated disease as compared to the Asian non-human primate species that do not demonstrate any detectable signs of lentiviral infection but who upon experimental infection with select SIV isolates from the African species develop clinical signs and laboratory based findings similar to human HIV-1 infection provide a powerful model to define virus-host relationships. It is our belief that unraveling those differences which are specifically associated with disease resistance and/or disease susceptibility culled out from those that are species specific differences unrelated to disease outcome may provide some important insights which maybe fruitful for the formulation of vaccine strategies. The purpose of this chapter is to provide the reader with a summary of the findings from our laboratory from the past decade using the naturally SIV infected sooty mangabey model aimed at ferreting out some of these differences. Some very important paradoxes exist with this naturally infected lentivirus model. Thus, it is difficult to determine why these species demonstrate highly effective immune responses but yet maintain very high viral loads. Why do these naturally SIV infected species not demonstrate the plethora of clinical symptoms ascribed to select proteins of the SIV such as 'tat', 'nef', and other viral proteins as do the rhesus macaques and humans to HIV? Most of the targets of such proteins are highly conserved and yet no detectable pathology? We submit that the naturally infected species has evolved over time with a highly regulated immune system (a perfect host/parasite relationship) that is sufficient to prevent pathology and not in the order to exhaust the immune system. In addition, the quality of the anti-viral immune response is of interest. Thus, the mangabeys demonstrate a clear skew in their cytokine based immune response towards a predominantly TH2 bias which we believe is the reason why this species of mangabeys among the many studied, is perhaps is the only species that is susceptible to M. leprae infection (see Dr. B. Gormus's chapter). Some of our working hypotheses that are aimed to provide explanations for some of these paradoxes are provided herein.

Impaired responses to Mycobacterium leprae antigens in rhesus monkeys experimentally inoculated with simian immunodeficiency virus and M. leprae.

Seven of eight rhesus monkeys (RM) coinfected with simian immunodeficiency virus (SIV) and Mycobacterium leprae harboured acid-fast bacilli (AFB) at sites of dermal inoculation and/or at disseminated sites at times of humane sacrifice (up to 270 days post-M. leprae inoculation) due to SIV-induced debilitation or, in one long term survivor's case, to date over 3 years post-M. leprae inoculation. Detectable AFB were cleared in biopsies of inoculation sites of RM inoculated with M. leprae alone after 63 days postinoculation; these sites have, so far, remained AFB-negative, thereafter. Compared to animals infected with M. leprae alone, RM coinfected with SIV plus M. leprae showed: 1, completely suppressed serum antibody responses to M. leprae-specific PGL-I antigen, but strong anti-SIV Gp120 antibody responses; 2, impaired sensitization of blood mononuclear cells (MNC) to in vitro recognition of M. leprae-specific antigens in blastogenic stimulation assays; 3, impaired in vitro responses of blood MNC to nonspecific (ConA) blastogenic stimuli; and 4, early post-M. leprae inoculation, there was a significant incremental diminution of percentages of blood CD4+CD29+ T-cells in addition to the existing SIV-induced diminished percentages of CD4+CD29+ T-cells. The results indicate that humoral and cellular immune responses to M. leprae antigens are compromised in M. leprae-inoculated RM previously infected with SIV. These results provide an immunologic basis for the demonstration of enhanced M. leprae persistence or leprosy susceptibility in SIV-M. leprae coinfected RM.