Background: The rate of immunological deterioration and progression to AIDS differs markedly between HIV-positive individuals, and may be influenced by cofactors, HIV phenotype and host T-cell response. Tumour necrosis factor (TNF)-alpha and lymphotoxin stimulate HIV replication and may induce apoptosis of HIV-infected and uninfected lymphocytes in vitro, thus accelerating disease progression and CD4 depletion. Variability in TNF production between individuals is to a degree genetically determined and may be predicted from polymorphisms of microsatellite regions surrounding the human TNF gene locus.
Methods: We examined TNf microsatellite polymorphisms in 24 HIV-positive patients with slower disease progression (CD4 count > 400 x 10(6)/l at > or = 6 years), 20 HIV-positive patients with faster progression (CD4 count < 200 x 10(6)/l within 5 years) and 109 healthy controls resident in north-west England. Typing was performed by polymerase chain reaction amplification of TNF a, b, c and d microsatellites and alleles were defined using fluorescence-based semi-automated microsatellite mapping techniques.
Results: No significant differences in TNF a, b and d allele frequencies were observed between faster and slower progressors, or with healthy controls. The frequency of the TNF c2 allele was significantly different between HIV-positive slower (60.9%) and faster (15%) progressors (P = 0.002) with an odds ratio of 0.1 (95% confidence interval, 0-0.6). TNF c2 was also less frequent in faster progressors than in healthy controls (45.9%, P = 0.006) with an odds ratio of 0.2 (95% confidence interval 0-0.8).
Conclusions: This is the first report demonstrating a strong association between the TNF c2 allele and the rate of HIV progression. Although it is possible that this finding may have arisen as a result of linkage disequilibrium with other alleles within the major histocompatibility complex that exert a more powerful effect upon progression, evidence is mounting to suggest that both TNF-alpha and lymphotoxin are closely involved in HIV disease progression and CD4 depletion. Our results serve to highlight the potential importance of genetic polymorphism, particularly of the TNF locus, in influencing the progression of HIV infection.