Differential Effects of HIV Type 1 Clade B and Clade C Tat Protein on Expression of Proinflammatory and Antiinflammatory Cytokines by Primary Monocytes

The existence of multiple subtypes of HIV-1 worldwide has created new challenges to control HIV-1 infection and associated neuropathogenesis. Previous studies indicate a difference in neuropathogenic manifestations of HIV-1-associated neuroAIDS between clade B- and clade C-infected subjects with clade B being more neuropathogenic than clade C. However, the exact mechanism underlying the differences in the neuropathogenesis by both the subtypes remains elusive. Development of neuroAIDS is associated with a complex interplay between proinflammatory and antiinflammatory cytokines and chemokines. In the current study, we hypothesize that HIV-1 clade B and C Tat protein exert differential effects on human primary monocytes leading to differences in gene and protein expression of cytokines implicated in neuroAIDS. Primary human monocytes were treated with clade B and clade C Tat protein and quantitative real time PCR was performed to determine gene expression of proinflammatory cytokines (IL-6 and TNF-alpha) and antiinflammatory cytokines (IL-4 and IL-10). Further, cytokine secretion was measured in culture supernatants by ELISA, whereas intracellular cytokine expression was detected by flow cytometry. Results indicate that monocytes treated with Tat B showed significant upregulation of proinflammatory cytokines, IL-6 and TNF-alpha, as compared to Tat C-treated cultures. However, expression of antiinflammatory molecules and IL-4 and IL-10 was found to be higher in Tat C-treated compared to Tat B-treated cultures. Thus, our result shows for the first time that Tat B and Tat C differentially modulate expression of neuropathogenic molecules that may be correlated with the differences in neuroAIDS manifestation induced by clade-specific infections.