Study On The Mechanism Of Natural Immunity In Atypical Monkey Immunodeficiency Virus (SIV) Infection

Background In different individuals, human immunodeficiency virus (HIV-1) infection causes differences in disease progression. More than95%of those infected appear typical disease progression, there are about5%HIV-1infected appear atypical disease progression, the performance after the viral infection is that viral load levels remain below the detection lines or appear later, no significant decline appears in the absolute number of CD4+T cells, disease progression shows atypical. In repeated low-dose mucosal infection monkey model of AIDS research, the researchers also found a similar situation. Some Rhesus monkeys, after the infection of Simian Immunodeficiency Virus (SIV)/Simian-Human Immunodeficiency Virus (SHIV), the appearance of plasma viral load delay and (or) the peak value decline significantly. Recent studies showed that the effect of cellular immunity, neutralizing antibody and other specific immunity is very limited, and innate immunity has been considered an important defense mechanisms at the early stage of virus infection, including phagocytosis of macrophages, ADCC (Antibody Dependent Cell Mediated Cytotoxicity) of NK cells and antigen presentation of dendritic cells, etc. But in the process of atypical HIV infection, the role and mechanism of the innate immune are still unclear.In addition, a class of innate immune molecules discovered recently is the host restriction factor; They coexisted with the the virus in a long period and evolved into a class of host anti-viral genes, including TRIM5a, APOBEC3G, Tetherin, SLFN11and so on. In vitro tests, they were able to suppress HIV effectively. SAMHD1is a newly discovered innate immune molecule, but the polymorphism of Rhesus samhdl gene and its effect on protein structure and function have not been reported.Methods The study will use repeated low-dose rectal mucosal infection with SIVmac239of Chinese rhesus monkeys as the animal model, to analyse the activation, proliferation and immune functions of CD4+T cells, NK cells and DC cells in typical and atypical disease progression by flow cytometry techniques, in order to discover the mechanisms of immune protection. On the other hand, by gene sequencing, sequence alignment, protein structure prediction techniques, the study plan to explore the cSNP on rhesus Samhdl gene and its impact on protein function, in order to recognise the SAMHD1protein antiviral mechanism better.Results By plasma viremia, SIVmac239infected Rhesus can be divided into three groups:typical infection, delayed infection, occult infection, regardless of the infection viral load. In the whole course of the disease, the absolute number of CD4+T cells of Occult group and delayed group is higher than the typical group, there were significant differences between the delayed group and the typical group. In the first14days of infection, three groups reached the lowest level of the absolute number of CD8+T lymphocyte, CD8+T lymphocytes of occult group and delayed group monkeys recover faster, there are significant differences between the delayed group and the typical group. In the acute phase of infection, CD4+Tem proportion of typical group monkeys maintained a higher level than the occult group, with a statistically significant difference. After21days of infection, Occult group CD4+Tem cells reduced proliferative activity and significantly smaller than the other two groups. IFN-y expression level of the occult group NK cells was significantly higher than the typical group, and the TNF-a expression level of delayed group was significantly lower than the other two groups, there were statistically significant. At the early stage of infection, in addition to the occult group, whose DC TNF-a expression level increased momently, other groups maintained a specific level and started to decline after39days of infection. Performed a transcriptome RNA sequencing analysis for these three groups of monkeys, there were two genes found directly associated with the innate immunity in the genes with highly significant difference.By sequence alignment,11mutations were found on Samhdl gene. There are five sites which are non-synonymous mutations:15bp (C/G),320bp (C/T),547bp (G/A),552bp (A/T),839bp (T/C) and determined the location of the five sites in the SAMHD1protein. Then used SNaPshot technology to confirm that these five non-synonymous mutations are SNP loci. While performed statistics of gene frequencies and each SNP locus genotype types and ratios of Rhesus Samhdl. Finally, by the biological prediction software, found that five non-synonymous SNPs affect the secondary structure of the protein and V280A sites may affect SAMHD1deoxynucleotide triphosphate hydrolase activity.Conclusion Atypical disease progression Rhesus macaques compared to typical disease progression Rhesus macaques, the former have:a higher absolute level of CD4+T cells and faster recovery capability of CTL cells; lower proportion of CD4+Tem:and proliferative activity; higher NK cell immune regulation capability by releasing IFN-y and higher levels of TNF-a released by DC cells. Inhibition of viral replication of these factors play an important role of atypical disease progression phenomenon. At least five SNP loci has been found in Chinese Rhesus monkeys SAMHD1protein, according to the predictive analysis, their presence affects the function of the protein, which provides a clue for a better understanding of SAMHD1antiviral function. This study initially identified the role and mechanism of the innate immune system in atypical SIV infection, which is of great significance for AIDS vaccine research and development, and disease control.