Cytokines regulate HIV-1 replication and lymphocyte apoptosis in vitro

Aim. To study the ability of cytokines - interleukin-2, interleukin-7 and tumor necrosis factor alpha to induce human immunodeficiency virus type 1 (HIV-1) replication and lymphocyte apoptosis in vitro. Methods. Peripheral blood mononuclears were separated by centrifugation on a ficoll paque solution specific density gradient. Lymphocytes were cultivated in RPMI 1640 medium with addition of L-glutamine, embryonal bovine serum, antibiotics and cytokines (interleukines-2, -4, -7, tumor necrosis factor alpha). To infect the lymphocytes, a laboratory strain of HIV-1 NL4-3 (NIH Res&Reag. Prog., USA) was used. HIV-1 replication was assessed by р24gag viral protein level in culture supernatants (ELISA) and its cytozolic level in lymphocytes (flow cytometry). Lymphocyte apoptosis was assessed by flow cytometry using the following parameters: (1) decrease of transmembrane mitochondrial potential; (2) increase in phosphatidyl serine molecules expression. Lymphocyte activation was assessed by CD25 and HLA-DR molecules expression (flow cytometry). Results. Cytokines induce the HIV-1 replication in lymphocytes in vitro. HIV-1 replication was noted only if inactivated lymphocytes were present in the culture. At the same time, lymphocytes not expressing the classical activation markers (CD25 and HLA-DR) were present among the lymphocytes producing HIV-1 indicating the possible alternative mechanism of HIV-1 replication, not dependent on cell activation. This fact might also be an evidence of viral replication processes in the pool of latently-infected lymphocytes, not expressing the classic activation markers. The abovementioned cytokines promote apoptotic death of uninfected lymphocytes in vitro, backing up the infected cells viability and thus promoting HIV-1 replication. Conclusion. Cytokines (interleukines-2, -4, -7, tumor necrosis factor alpha) which are known as factors supporting the immune system homeostasis and immune response formation, might also play a negative role in HIV-1 pathogenesis - induce HIV-1 replication in lymphocytes and, probably, lead to reactivation of the pool of latently-infected lymphocytes, deepening the lymphopenia and leading to disease progression.

HIV-infection, cytokines, viral replication, lymphocytes, apoptosis, HIV latently-infected cells