Soluble CD4 during human HIV-1 infection

The CD4 antigen has long been used as a surface marker for the indentification of a subset of T cells. CD4 acts also as the receptor for the Human Immunodeficiency Virus 1 HIV-1 and as a signal transducing molecule. Recently CD4 positive cells have been shown to release a soluble form of CD4 (sCD4). This molecule can interact with free gp 120 viral antigen and with serum immunoglobulins. Because of the importance of CD4 in the natural history of HIV-1 infection, we decided to monitor it's serum levels in HIV-1 seropositive subjects. sCD4 increases, on a per cell basis, in the late stages of infection, when CD4 cell counts dramatically fall and antigenemia is frequently found. Asymptomatic patients had a mean of 6 Units/ml of sCD4 every 100 CD4 T cells, while in AIDS patients we found a mean of 51 Units/ml every 100 CD4 T cells. These data suggest that sCD4 may be of value in monitoring the involvement of CD4 T cells during a pathological event.