Lymphoid cell resistance to glucocorticoids in HIV infection

In humans infected with the HIV-1 virus there may be a disproportionate severity of signs and symptoms of illness compared to the fraction of CD4+ infected T-lymphoid cells. In part, this may be due to altered intercellular signalling systems and intracellular signal transduction. Glucocorticoids are well known for their effects on the vitality and function of lymphoid cells. Patients with HIV infections often show elevated circulating levels of cortisol, suggesting some misfunction in the regulatory systems that maintain the levels of this critical hormone. At the cellular level, it is known that both acute HIV infection and glucocorticoids can cause apoptotic cell death in thymic lymphocytes. However, chronically HIV-infected cells appear to be resistant to glucocorticoid-evoked cell death. Glucocorticoid receptor-ligand binding studies on patients' cells have shown reduced affinity between the receptor binding sites and test steroids. In vitro, chronically HIV-infected cells of the lymphoid CEM line displayed resistance to glucocorticoid-induced apoptosis. These cells showed reduced numbers of binding sites with little alteration in apparent affinity between ligand and receptor. Thus it appears that there may often be malfunction of the normal glucocorticoid response in HIV-infected cells probably due to altered interactions between the glucocorticoid receptor and its hormone. Such alterations may have clinical consequences, including the possibility of a relatively longer life span of infected CD4+ T-lymphocytes, as well as systemic effects of chronically elevated cortisol level.