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 inhibitors. 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 gamma-IFN induction. Thus KG-1 myeloblast cells express all
class II antigens (DR greater than DP greater than DQ) constitutively and their expression increased after gamma-IFN treatment. KG-1a, an immature blast variant of KG-1, does not express
class II antigens, even after gamma-IFN treatment. THP-1, a monocytic cell line expresses DR but not DP or DQ under basal conditions. DP and DQ are, however, gamma-IFN inducible. The class II negative HL-60 promyelocytic cell line, expresses DR and DP but not DQ after gamma-IFN induction. In all the above cell lines, surface expression of
class II antigens correlated with the levels of
mRNA expression as determined 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 gamma-IFN, however, specific
mRNA message was observed under basal conditions and was further increased with gamma-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.