Background:  We previously reported that HIV actively replicates in primary CD4⁺ Th0 cells (IFN-g⁺IL-4⁺). It was unclear whether HIV preferentially infect Th0 cells or replicate in both Th1 (IFN-g⁺IL-4^­ ) and Th2 (IFN-g^-IL-4⁺) cells but alters their profile to a Th0 phenotype. We evaluated whether preferential infection or a cytokine alteration pathway is responsible for the observed prevalence of HIV within primary CD4⁺ Th0 cells.

Methods:  CD4⁺ T cells were infected with HIV and co-expression of p24 within Th2, Th1, or Th0 cells was monitored by flow cytometry. The CRTH2 marker, a prostaglandin receptor selectively expressed on Th2 cells, and intracellular immunostaining for prototypical Th1/Th2 cytokines (INF-g, IL-4, TNF-a, and IL-10) were used to discriminate between the various Th subsets. Cell activation status was evaluated by expression of CD95, HLA-DR, CD25, CD69, and CD45RO. A cohort of 13 HIV⁺ patients, with CD4 counts ranging from 90 to 896 cells/mL were also examined for CRTH2 expression on CD4⁺ T cells and for the frequency of Th0, Th1, and Th2 phenotypes within CD4⁺CRTH2⁺ (Th2) and CD4⁺ CRTH2^­ (Th1/Th0) T cells.

Results:  We confirmed that Th2 cells express the prostaglandin receptor CRTH2, as demonstrated by induction of IL-4 expression to approximately 70% in only CRTH2⁺ cells post-mitogen stimulation. The frequency of CD4⁺ CRTH2⁺ T cells was approximately 2% in peripheral blood. Post-infection, independent of the virus isolate used, a greater level of HIV replication was present in the Th2 (CRTH2⁺ cells) than the CRTH2^­ subset, as indicated by p24 staining. Using co-staining for prototypical Th cytokines and p24 indicated that HIV was predominantly in Th0 and Th2 cells, while Th1 cells expressed minimal levels of HIV. HIV infection increased IFNg production among Th2 cells and IL-4 production among Th1 cells, demonstrating a shift to a Th0 phenotype. Robust infection in Th2 cells was associated with higher level of activation. In comparison to healthy individuals, HIV⁺ patients exhibited a decline in Th2 cells and a shift towards a Th0 phenotype, confirming the in vitro infection data.

Conclusions:  Data indicate that HIV-productive replication in Th2 or Th1 cells induces a Th0 phenotype. This may be an inherent result of HIV-mediated potent cell activation or a deliberate mechanism to overcome the skewing of the immune response, the immunologic consequences of which remains to be elucidated.

Keywords: Cytokines; pathogenesis; HIV replication