With regard to HLA class 1 antigen:
a. they are expressed on all nucleated cells
b. they are essential for viral antigen recognition by cytotoxic cells
c. the genes for HLA class 1 molecules are located on chromosome 6 and 15
d. all above
a. they are expressed on all nucleated cells
b. they are essential for viral antigen recognition by cytotoxic cells
c. the genes for HLA class 1 molecules are located on chromosome 6 and 15
d. all above