Spontaneous proliferation of HTLV-II-infected peripheral blood lymphocytes: HLA-DR-driven, IL-2-dependent response

Peripheral blood lymphocytes obtained from HTLV-II-infected persons (n = 13) and cultured in the absence of exogenous stimulator demonstrated augmented spontaneous proliferation (17,672 +/- 5,498 cpm) when compared with cells from healthy donors (1,921 +/- 1,306 cpm). Removal of non-T population did not abrogate the proliferative response of patients' PBMC, suggesting that the proliferation is not related to the autologous mixed lymphocyte reaction. Addition of recombinant interleukin-2 (rIL-2; 0.1 U/ml) to spontaneously proliferating cultures from HTLV-II-infected persons resulted in a 3- to 4-fold increase in proliferation (61,985 +/- 16,003); in contrast, PBMC from controls demonstrated 38- to 42-fold increase in their proliferative capacity in response to rIL-2 (77,256 +/- 13,044). Antibodies to both IL-2 receptor and HLA-DR were able to inhibit the spontaneous proliferation of PBMC from HTLV-II-infected persons in a dose-dependent manner. Furthermore, addition of cyclosporin A, which preferentially blocks accumulation of IL-2 mRNA, also inhibited spontaneous proliferation in a dose-dependent manner. These observations suggest that the spontaneous proliferation of HTLV-II-infected PBMC is at least in part an HLA-DR-driven, IL-2-dependent event, which is not analogous to the AMLR.