Figure 2.

(a, b) Haematopoietic progenitor cells (HPCs) poorly express MHC antigens. (a) To determine MHC expression by HPCs, cells were stained with either an anti-class I or an anti-class II antibody. In addition, HPCs that had been previously treated with interferon-γ (IFN-γ) were also included. Class I expression by HPCs was greatly increased by IFN-γ, but not that of MHC class II antigens. These results are also displayed as dot plots in (b). (c) HPCs were used as target cells against anti-H2-L^d alloreactive T cells. BALB/c concanavalin A (Con A) blasts were readily lysed, but not the BALB/c HPCs (n = 5). The 129SvJ HPCs were used as controls. (d) Since the HPCs were not lysed by cytotoxic T lymphocytes, we pulsed the HPCs with either the H2-L^d-specific QL9 peptide or with a scrambled OVA peptide and used these HPCs as target cells. None of these cell types was lysed by the HPCs (n = 5). All experiments were performed in triplicate. Con A blasts were again used as positive controls.