The relation between B-cell stimulation and delayed hypersensitivity. The effect of cyclophosphamide pretreatment on...

Cyclophosphamide (CY), which can enhance some forms of delayed-type hypersensitivity if given 3 days before immunization, is also a potent suppressor of most antibody mediated 4-h skin reactions to protein antigens. However many haemagglutinating antibodies, which are present in serum at the time of skin testing, are not similarly suppressed. Antibody titres in some sera recovered from CY-pretreated guinea-pigs differ little from titres in control sera. This resistance to CY suggests that long-lived precursors characterize the B-cell lines that produce many haemagglutinating antibodies, whereas the CY-sensitive precursors of skin reactive antibodies, which mediate Arthus-type reactions, are probably rapidly dividing, short-lived cells. Furthermore, the novel appearance of BGG antibodies in sera from CY-pretreated animals immunized with DNP50-BGG indicates that haemagglutinating antibody responses to some antigens are regulated by CY-sensitive mechanisms.