In addition to acquired immunodeficiency syndrome (AIDS), persons infected with human immunodeficiency virus often develop cutaneous manifestations, including severe psoriasis. In previous studies, we have established that psoriatic fibroblasts and erythrocytes obtained from psoriatic patients exhibit decreased levels of cyclic adenosine monophosphate (cAMP) dependent protein kinase (PKA) activity and of 8-azido-[32P]cAMP binding to the RI and RII regulatory subunits of PKA. Because treatment of patients with peptide T (an octapeptide sequence found in the human immunodeficiency virus envelope glycoprotein gp120) has been observed to result in an improvement in the psoriatic condition, studies were initiated to determine if peptide T and gp120 protein treatment of normal and psoriatic human fibroblasts resulted in any changes in PKA. Exposure of psoriatic fibroblasts to peptide T resulted in a time (4 h to 6 d) and dose [10(-14)-10(-8) M] dependent increase in the levels of 8-azido-[32P]cAMP binding to the RI and RII regulatory subunits of PKA, along with a corresponding increase in PKA activity. Peptide T exhibited a biphasic dose dependent response, with maximal effects on PKA noted at 10(-12)M peptide T. Treatment of normal human fibroblasts with peptide T did not result in any change in PKA levels. Conversely, treatment of normal human fibroblasts for 18 h with gp120 protein [10(-13) M] resulted in a significant decrease in the levels of 8-azido-[32P]cAMP binding to RI and RII and in PKA activity. The presence of peptide T blocked this effect of the gp120 protein. These results indicate that peptide T and gp120 protein may inversely alter the intracellular levels of 8-azido-[32P]cAMP binding to RI and RII, and of PKA activity in susceptible cells. These observed changes in the cyclic AMP-PKA signaling pathway, a biochemical marker for psoriasis, may offer some mechanistic insight into the noted beneficial effects of peptide T treatment, including an improvement in psoriatic lesions.