Titration of an SIVmac251 stock by vaginal inoculation of Indian and Chinese origin rhesus macaques: Transmission efficiency, viral loads, and antibody responses

The purpose of this study was to determine whether rhesus monkeys of Chines e origin are suitable for studies of mucosal lentivirus transmission by com paring the relative ability of these animals and rhesus macaques of Indian origin to become infected by vaginal (IVAG) inoculation with SIVmac251. In addition, we sought to test the hypothesis that differences in viral load d uring the first few weeks after inoculation were due to the relative streng th of the anti-SIV immune responses in the two populations of rhesus macaqu es. Significant difference was not observed between the number of Indian an d Chinese origin monkeys that were infected after IVAG SIV inoculation in t his study. For 8-9 weeks after infection there was considerable overlap in the range of viral loads among the Indian and Chinese animals and the varia tion among the Indian origin animals was greater than the variation among t he Chinese origin monkeys. By 6 weeks postinfection, viral loads in SIV-inf ected Chinese origin monkeys tended to be at the lower end of the range of viral loads observed in SIV-infected Indian origin monkeys. The strength of the anti-SIV antibody response was also more variable in the Indian origin rhesus macaques, but at 6-8 weeks postinfection, Chinese and Indian origin rhesus macaques had similar titers of anti-SIV antibodies. Microsatellite allele frequencies differed between Chinese and Indian rhesus macaques; how ever, the majority of alleles present in Indian-origin animals were also fo und in Chinese macaques. Together these results show that host factors, oth er than geographic origin, determine the ability of a rhesus macaque to be infected after IVAG SIV exposure and that geographic origin does not predic t the viral load of SIV-infected animals during the first 8-9 weeks after I VAG inoculation.