Prior to this study, no polymorphisms in the TLR7
gene locus of rhesus macaques were known. We therefore re-sequenced the TLR7
gene in 36 rhesus macaques of Indian origin and identified 12 polymorphisms. An initial analysis of 36 monkeys revealed three tightly linked SNPs to be associated with disease progression. Subsequent investigation of a larger sample of SIV-infected monkeys confirmed this initial result. The polymorphisms were significantly associated with viral load at set-point in untreated-SIV-infected male rhesus macaques and showed a trend towards an association with survival time even after the exclusion of monkeys carrying MHC
alleles associated with rapid or slow disease progression. One of the polymorphisms of interest is located in the 3′ UTR region of the TLR7
mRNA, one is a silent nucleotide substitution located at amino acid position 570, and the remaining variant encodes a non-synonymous amino acid substitution (5VM) in the leader peptide. Formally, we could not distinguish which of these tightly linked polymorphisms may be responsible for the differential viral load. Furthermore, each of the three types of genetic variation seen in TLR7
is known to affect protein expression. Mutations in the 3′UTR , for instance, can influence mRNA stability 
, silent mutations may influence translation efficiency and protein folding 
, and variations in the signal peptide can effect the transport, localization and synthesis of membrane-bound proteins 
The c.13G>A (V5M) SNP in the signal peptide represents a conservative exchange in the hydrophilic N-terminal region of the signal peptide. Using the SignalIP program 
, we found no evidence that the polymorphism would greatly influence processing of the signal peptide, although this cannot be ruled out completely without additional experimental evidence. In contrast, the 11L (rs179008
) substitution in the human TLR7 signal peptide is potentially capable of altering signal peptide function (see supplement ref 
). More convincing results were obtained in an analysis of RNA secondary structure. The rhesus c.13A
allele very likely destabilizes an RNA secondary structure predicted for the c.13G
allele. Interestingly, a strong RNA secondary structure comparable to the rhesus wild-type sequence was not predicted for the human TLR7
signal peptide RNA sequence, and it is unlikely that the Q11L (rs179008
) polymorphism will affect the secondary structure of the signal peptide-encoding RNA sequence. Furthermore, neither the silent mutation at amino acid position 570 nor the substitution in the 3′ UTR altered the potential secondary structure of the RNA around the respective SNPs. Based upon these predictions, the rhesus macaque c.13A
allele is a functional candidate for the observed association with higher viral load in untreated-infected macaques 
. This result encouraged us to also investigate the influence of an adjacent polymorphism at position −17
, which may affect the same local RNA structure and resides in a region critical for translation initiation. In silico
analyses predicted that the effect of c.-17C>T upon RNA secondary structure was dependent upon the nucleotide present at position 13. Notably, c.-17C>T was associated with differential survival time only in c.13G
carriers. Although translation represents a dynamic process that cannot be captured by mere sequence analyses, the coincidence of in silico
prediction and experimental data therefore suggests that both SNPs exert a synergistic influence upon RNA structure.
It should be noted that, in whole genome screens involving human HIV-1-infected patients 
, the association between human TLR7
SNPs and disease progression did not attain statistical significance after Bonferroni correction. The validity of the respective associations has therefore been questioned 
. While variation in the MHC
region is undoubtedly the most important host factor for determining disease progression, however, it explains only a fraction of the variability in HIV viremia 
. The identification of additional host gene polymorphisms contributing weakly to the variability of viremia or time to treatment initiation will require much larger cohorts and, because of the variability of the virus, the exact size of meaningful cohorts of HIV-1-infected patients may not even be known. We therefore proposed cross-species comparisons as a valuable means to validate potential host gene polymorphisms influencing the course of HIV-infection 
. This report is the third one describing similar effects of co-localising functional genetic polymorphisms in humans and rhesus macaques even although the affected biochemical pathways may differ between the two species 
. For TLR7
, the rhesus substitution at position 13 and −17 are more likely to influence translation efficiency whereas the human Q11L variation probably influences transport or localization. At last, however, both variants would affect TLR7 expression.
Most interestingly, the TLR7 polymorphisms did not influence plasma viral set-point and survival time in immunized macaques. One explanation for this result could be that vaccination-induced immune reactions such as T and B cell response had a much stronger influence upon viral replication than differential TLR7 expression.
To better define the influence of TLR7 polymorphisms on vaccine efficacy, larger numbers of macaques treated with the same AIDS vaccine are required. Furthermore, it is paramount to investigate the exact contribution of the polymorphisms on TLR7 expression and cytokine secretion in vitro and in vivo, in untreated and infected, and in immunized subjects. Our work highlights the dual role of TLR7 in immunodeficiency virus infection and vaccination. Assuming that the c.13A and c.-17T,c.13G variants are associated with enhanced TLR7 expression, the data suggest that efficient triggering of TLR7 may improve AIDS vaccine efficacy while attenuating the action of TLR7 may decelerate disease progression. Finally, our results imply that it may be important to control human vaccine trials, not only for MHC genotype, but also for TLR7 genotype.