Abstracts 125

orescence staining KG-1 cells expressed all the three class II HLA antigens. HL- 60 and U-937 cells did not express any of the class II antigens. Recombinant gamma interferon (BIOGEN) induced class II antigen expression on these cell lines. HL-60 cells expressed DR and DP but no D Q antigens. U-937 cells ex- pressed only DR. Nor thern analysis of HL-60 RNA revealed that gamma inter- feron induced mRNA transcripts hybridizing with alpha and beta chains of DR and DP as well as beta chain of DQ. These results indicate that myelomonocytic cell lines, like the normal myeloid progenitor cells, show a differential expression of class II HLA antigens. The constitutive and inducible expression of these antigens in the leukemic cell lines thus offers a system in which to analyze the regulatory factors involved in the differential expression of the genes of this multigene family.

Ia GENE EXPRESSION IN BONE MARROW CHIMERAS UNDERGOING GRAFT VS. HOST DISEASE. P Michael Stuart and Jerold G. Woodward; University of Kentucky Medical School, Lex- ington, KY

The focus of this project was to determine the Ia expression of nonbone marrow derived (NBMD) cells in bone marrow chimeras during graft-vs-host disease (GVHD). Serological detection of Ia antigens on N B M D cells has been shown to occur in several organs during G V H D but it has not been established whether these findings are the result of Ia gene expression or passive attachment of Ia antigens to N B M D cells that were shed from BMD cells. We have addressed this issue by producing bone marrow chimeras in which the genotype of the N B M D component (B10.A) has a functional E~ gene while the bone marrow cells (B10.A(4R)) do not, enabling our detection of N B M D Ia gene activity. These chimeras were subjected to G V H D 100 + days after irradiation and bone marrow reconstitution and sacrificed 8, 9, and 10 clays later. The organs of these animals were homogenized and RNA extracted and subjected to Nor thern Blot analysis. We observed Ec~ gene expression in the kidney, lung, and heart but no expression in the liver, skin, or spleen of these animals, while all organs, with the exception of liver, displayed As gene expression. When Eoi expression was compared to control chimeras, the expression in these organs was seen to be markedly increased, particularly with regard to heart which did not demonstrate hybridization in the control blot. These results suggest that Ia genes in N B M D cells of kidney, lung, and heart are induced during G V H D and that N B M D cells of the liver, spleen, and skin do not show such induction in our assay system.

INDUCTION OF HLA CLASS II ANTIGENS ON NORMAL HUMAN MELANOCYTES BY T R A N S F O R M A T I O N WITH RAS ONCOGENES. Janet S. Lee, Clifford R. Hume, Alan N. Houghton, and Anthony P, Albino; Memorial Sloan-Kettering Cancer Center, New York, N Y

Class II major histocompatibility antigens are expressed primarily on cells that function in the generation and regulation of an immune response, primarily B cells, macrophages, dendritic cells, and activated T cells. However , class II genes may be induced on many cell types, including melanocytes, by gamma interferon. Class II antigens are also expressed on many melanomas, the malignant coun- terparts of melanocytes; and about 10% of melanomas contain activated ras oncogenes. This correlation prompted us to investigate the function of activated ras genes in melanocyte lineage and to determine whether the ras oncogene products could induce the expression of phenotypic markers characteristic of