Perforin is not co-expressed with granzyme A within cytotoxic granules in CD8 T lymphocytes present in lymphoid tissue during chronic HIV infection

Background: Residual HIV-l-infected cells are poorly eliminated from lympho id tissue (LT) reservoirs by effector cytotoxic T lymphocytes (eCTL) despit e antiretroviral therapy. Perforin and granzyme A (grA) constitute major ef fector molecules within eCTL granules that induce apoptosis and lysis of vi rally infected cells. Objective: Expression of perforin and grA was studied at the single cell le vel in LT and blood from 16 patients infected with HIV-1 (stage A1-C) who w ere not taking antiretroviral therapy. Method: Immunohistochemical analysis by in situ imaging of cells from blood and LT. Results: Quantitative in situ imaging showed that perforin-expressing CD8 T cells comprised 0.3-1.5% of total cells within the LT from recent HIV-1 se roconverters, while grA was found in 2.1-7.2% of total cells. However, desp ite high-level grA upregulation (1.5-4.5% of total cells) compared with tha t in non-infected individuals (0.4-0.9%), perforin expression remained low (< 0.1% of total cells) (P < 0.02) in LT from patients with chronic HIV-1 i nfection (stage A2-C). This contrasted with findings in peripheral blood mo nonuclear cells (PBMC) from the same HIV-1 infected cohort where perforin w as detected in 13-31% of all PBMC, which was 10- to 100-fold higher than in lymphoid tissue (P < 0.001); grA was found in 14-32% of total PBMC. Two-co lour staining showed that granular expression of perforin and grA was restr icted to CD8 T cells in over 90% of total cells in both LT and blood. Conclusions: These findings indicate that cytotoxic perforin expression is impaired at local sites of HIV replication within lymphoid tissue. Since pe rforin is required together with grA for granule-mediated cytolysis, the lo w perforin expression in the LT may limit the ability of eCTL to eliminate HIV-1 infected cells in lymphoid tissue. (C) 1999 Lippincott Williams & Wil kins.