This is the first time, to our knowledge, that evidence is presented showing that a polyantigenic immunomodulator (PAI), acting as a biological response modifier, can either induce or suppress HIV expression depending on the viral load of infected PBMC. PAI consists of a mixture of inactivated bacteria with influenza virus vaccine. PBMC from HIV-infected patients (asymptomatic, age 22-36, symptomatic, age 30-59 and pediatric, < 2 years old) were co-cultured with PHA-stimulated PBMC from uninfected individuals in medium containing IL-2 and PAI. Parallel co-cultures were carried out in a PAI-free medium. Cultures were fed with PHA-stimulated PBMC from uninfected donors on a weekly basis. HIV-p24 ag and cytokine profiles (IL-1 beta, IL-2, IL-4, IFN-gamma and TNF-alpha) were determined on supernatants on day 14. Peripheral blood samples from each patient were evaluated at the beginning of the experiment as to total CD3, total CD19, CD3/CD4, CD3/CD8, CD16/CD56, CD8/HLA-DR and CD8/CD38 markers through flow cytometry. PAI was able to induce viral expression (up to 11,881 pg/ml of p24 antigen) in cultures showing a low (less than 16 pg/ml) or no viral titer. In contrast, in those cultures with high viral titer (10(2)-10(5) pg/ml), a substantial reduction on the titer was observed upon exposure to PAI. PAI was able to induce the production of IFN-gamma and TNF-alpha while that of IL-4 and IL-1 beta was reduced. The predominant cell type detected in the blood samples of the studied subjects were CD8+, CD8+/CD38+ or CD8+/HLA-DR+.(ABSTRACT TRUNCATED AT 250 WORDS)