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

Abstract

The purpose of this study was to determine whether rhesus monkeys of Chinese origin are suitable for studies of mucosal lentivirus transmission by comparing 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 during the first few weeks after inoculation were due to the relative strength of the anti-SIV immune responses in the two populations of rhesus macaques. Significant difference was not observed between the number of Indian and Chinese origin monkeys that were infected after IVAG SIV inoculation in this 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 variation among the Indian origin animals was greater than the variation among the Chinese origin monkeys. By 6 weeks postinfection, viral loads in SIV-infected 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; however, the majority of alleles present in Indian-origin animals were also found in Chinese macaques. Together these results show that host factors, other than geographic origin, determine the ability of a rhesus macaque to be infected after IVAG SIV exposure and that geographic origin does not predict the viral load of SIV-infected animals during the first 8-9 weeks after IVAG inoculation.

Fig. 1

Comparison of in vitro titration of SIVmac251-5/98 stock in primary PBMCs from Indian and Chinese origin rhesus monkeys. Note that the range of p27 antigen levels in PBMCs from all of the animals is similar.

Fig. 2

SIV RNA levels in plasma of rhesus macaques of Chinese and Indian origin.

Fig. 3

(A) Levels of SIV RNA in plasma 2 and 6 weeks after IVAG inoculation for macaques of Chinese origin (filled symbols) and Indian origin (open symbols). The means (indicated by arrows) for Chinese and Indian origin animals are significantly different at 6 weeks postinfection, but not at 2 weeks postinfection (see Table 3). (B) Decrease in SIV RNA plasma levels from 2 to 6 weeks after IVAG inoculation with SIV for macaques of Chinese origin (filled symbols) and Indian origin (open symbols). The means (indicated by arrows) for Chinese and Indian origin animals are significantly different (see Table 3).