HIV-1 p24 antigen can be detected in the CSF of seropositive individuals with dementia more frequently than in non-demented subjects. A high degree of amino acid sequence homology has been demonstrated to exist between HIV p24 and transthyretin (TTR), a molecule which binds T4, T3 and the retinol/retinol-binding protein complex (holo-RBP). The long term goals of this proposal are to determine if the structural similarity between TTR and HIV-1 p24 can be associated with antigenic cross- reactivity between TTR and HIV p24, impaired TTR function, and altered localization and synthesis of TTR in individuals with HIV-related neurologic disease. The aims of the proposed project are (1) to characterize HPLC protein fractions in CSF samples and to quantitate TTR an dp24 antigen levels in the protein fraction and in blood of seropositive individuals with and without dementia and in individuals are cross-reactive with TTR and to develop sensitive assays for detecting p24 antigens in samples that are negative for p24 antigen using currently available assays (3) to determine if specific binding occurs between TTR and HIV-1 p24 antigen and whether HIV-1 p24 antigen competes with the binding of TTE to T4 and holo-RBP; and (4) to quantitate TTR, p24 antigens, and messenger RNA (mRNA) levels for these molecules in liver and nervous system tissue lysates from seropositive individuals and seronegative controls will be separated using HPLC ion exchange chromatography followed by identification of protein species in the fractions on electrophoretic gel and immunoblots and by quantitation of protein species in the fractions on electrophoretic gels and immunoblots and by quantitation of p24 antigen and TTR in immunoassays. Antigenic cross-reactivity between p24 antigen and serum, human TTR, and recombinant HIV-1 p24 and p24 peptides. The ability of p24 antigen to inhibit TTR binding to thyroid hormone and RBP will be assayed in competitive binding studies. Tissue levels of TTR, p24 antigen, and specific mRNA will be measure in antigen capture ELISA assays and using the polymerase chain reaction assays, respectively. The morphologic localization of antigen and mRNA will be determined using immunocytochemical and in situ hybridization techniques.