Natural antibodies to HIV-tat epitopes and expression of HIV-1 genes in vivo.

The tat regulatory protein of HIV-1 was expressed as a fusion protein in E. coli and used as antigen to detect antibodies against HIV-tat (anti-tat) in the serum of HIV-1 infected children and adults. HIV-1-infected children showed a higher frequency (55%) of anti-tat than HIV-1-infected adults (36%). Anti-tat were present in only 15% (3/20) of acutely infected individuals. Forty percent (10/25) of individuals with prolonged HIV-1 infection but without antigen were anti-tat positive. Only 13% (3/23) of HIV-1-antibody-positive individuals with prolonged HIV-1 antigenemia were anti-tat positive and titers of anti-tat antibodies declined with time. Pepscan analysis identified the amino terminus of HIV-tat as the major antibody-binding site. Antibodies to HIV-tat occurred as a harbinger of HIV-1 antigen expression and disappeared thereafter, possibly reflecting the transience of HIV-tat expression. Because of the low antigenicity of HIV-tat, antibodies to this regulatory protein are not a reliable marker for either early HIV-1 infection or subsequent disease progression.