The presence of serum cholinoreceptor autoantibodies in HIV infected patients, which are related to the stage of the disease evolution was demonstrated. By ELISA using synthetic peptide corresponding to the aminoacid sequence of the second extracellular loop of human M₁ muscarinic acetylcholine receptors (mAChR), we detected that the optical density values and frequency of serum anti M₁ mAChR antibodies were higher in HIV+/AIDS patients than HIV+ asymptomatic patients. Sera from HIV- non infected individual yield negative results. Significant correlation between M₁ mAChR autoantibodies titres of each patients and the decrease in CD4+ cells and the increase of viral load was observed. Moreover, the affinity purified anti M₁ peptide IgG was able to react with CD8+ T cells triggering the production of large amount of PGE₂ from the cells. The antibody-lymphocyte interaction through the release of PGE₂, acting as immunomodulator could maintain the immunosuppressive cell response described in AIDS patients.