Differential expression of MHC class II antigens in myelomonocytic leukemia cell lines

Major histocompatibility complex (MHC) class II antigens are discordantly expressed on hematopoietic progenitor cells. Their expression is linked to differential responsiveness of the cells to growth factors and inhibitiors. We examined the expression of different MHC class II antigens in a panel of human myelomonocytic cell lines representing different stages of differentiation, by cytofluorographic analysis with monoclonal antibody (MoAb) and Northern blot analysis with specific cDNA probes. These analyses revealed discordant expression of different MHC class II antigens both in basal state and after γ-IFN induction. Thus KG-1 myeloblast cells express all class II antigens (DR > DP > DQ) constitutively and their expression increased after γ-IFN treatment. KG-1a, an immature blast variant of KG-1, does not express class II antigens, even after γ-IFN treatment. THP-1, a monocytic cell line expresses DR but not DP or DQ under basal conditions. DP and DQ are, however, γ-IFN inducible. The class II negative HL-60 promyelocytic cell line, expresses DR and DP but not DQ after γ-IFN induction. In all the above cell lines, surface expression of class II antigens correlated with the levels of mRNA expression as determinated with specific cDNA probes. In U-937, a monocytic cell line, no surface expression of class II MHC antigens was observed either with or without γ-IFN, however, specific mRNA message was observed under basal conditions and was further increased with γ-IFN, indicating a possible defect in assembly or transport of class II antigens. The patterns of class II MHC antigens in these leukemic cell lines may be a useful model to delineate molecular basis of discordant MHC class II expression during myelomonocytic differentiation.