Development and Application of Immunoassays To Detect and Characterize p7 Immunogenicity in HIV-1 Infected Populations

Abstract

The primary objective of this study was to characterize the immunogenicity of the HIV-1 nucleocapsid protein, p7, in animal and human populations. To examine this (1.) dot blot and ELISA p7 antibody detection assays were developed and optimized, (2.) rabbit hyperimmune p7 antisera was characterized for p7 antibody reactivity using both the dot-blot and ELISA immunoassays, (3.) frozen serum samples from high-risk populations which were previously well characterized for antibodies to HIV-1 major viral antigens were screened for p7 antibodies using the dot-blot assay, and (4.) serial samples from several subjects were characterized for anti-p7 relative to time to develop a pattern of seroconversion. No attempt was made to correlate clinical symptoms with p7 antibody reactivity. Results of this study demonstrate that (1.) purified p7 is able to stimulate the development of high titers of specific antibodies in rabbits, (2.) HIV-1 infected human subjects develop significantly different/lower p7 antibody reactivity than the p7 immunized rabbits, (3.) the anti-p7 human antibodies can be detected by the dot-blot immunoassay but not the ELISA immunoassays developed for this study, (4.) the mode of HIV-1 transmission may be important for the development of antibodies to p7, (5.) HIV-1 infected human subjects develop significantly lower p7 antibody reactivity than antibodies to the major HIV-1 antigens used in standard ELISA and RIA assays, and (6.) once anti-p7 is established, it persists, but duration of infection does not appreciably increase p7 antibody levels. Given the relatively low immunogenicity of p7 in human subjects, a p7 antibody detection assay would be an unreliable HIV-1 diagnostic tool but a p7 antigen capture assay might be very useful. Using this protein rather than p24 as a marker would eliminate the problem of extensive immune complex formation. However, the use of p7 antigen as a sensitive marker for plasma viremia, will depend on its presence and form in plasma. Although the results of this study suggest that HIV p7 is not sequestered within antibody-antigen complexes, it may be sequestered within whole virions, core antigens, infected cells, or all three. Additional studies are needed to determine if p7 antigen in serum is available for capture in an antigen-capture assay.