Absence of major histocompatibility class II expression does not impair hematopoiesis in mice

Objective. Major histocompatibility class II (MHC II) molecules are among t he earliest antigens to be expressed in hematopoietic progenitor cells; how ever, the functional role of these molecules in hematopoiesis remains contr oversial. We examined the role of MHC II antigens during hematopoiesis usin g a mouse model of MHC II deficiency related to the absence of the critical transcriptional activator, CIITA. Methods. Sca-1(-), Sca-1(+)lin(+), and Sca-1(+)lin(-) populations of marrow cells from CIITA(-/-) and wild-type mice were analyzed by immunofluorescen ce for MHC II expression. Hematopoietic capacity was assessed in CIITA(-/-) and wild-type mice by CFU-S, CFU-GM, and radiation sensitivity assays. Results. Flow cytometric characteristics of hematopoietic progenitors from CIITA(-/-) and wild-type mice were identical except for the absence of MHC II expression in CIITA null mice. There were no significant differences in capacity for hematopoietic reconstitution and clonogenicity as measured by radiation sensitivity, CFU-S, and CFU-GM assays among CIITA(-/-) and wild-t ype mice. Conclusions. These experiments show that downregulation of MHC II gene tran scription does not effectively alter normal hematopoiesis, and provide stro ng evidence that MHC II expression on hematopoietic progenitors is not requ ired for normal hematopoietic development. (C) 2001 International Society f or Experimental Hematology. Published by Elsevier Science Inc.