Receptors for antigen on lymphoid cells. II. The nature of the molecule responsible for plaque-forming cell adherence.

The nature of specific adherence of rat anti-TNP PFC to TNP-GRBC has been investigated with PLL-fixed antigen monolayers as cellular immunoadsorbents and as plaque indicators. The immunoglobulin nature of the molecule responsible for PFC adherence is suggested by the fact that pretreatment of the PFC with rabbit anti-rat Ig antisera, but not anti-histocompatibility antisera, inhibits adherence. Removal of the adherence capacity of early PFC with the proteolytic enzymes papain and pronase, or by "capping" with anti-Ig is followed by slow regeneration of the ability to adhere, suggesting that adherence is due to membrane rather than secreted immunoglobulin, the latter being detectable within minutes after enzyme treatment. Several time-related events relating to PFC adherence were observed. 1) Both direct and indirect PFC are capable of specific adherence; the ability to adhere, however, tends to decline with time, especially after secondary immunization. 2) Although early PFC adherence is unaffected by trypsin treatment, later populations become increasingly sensitive. 3) Pretreatment of PFC at various times after primary immunization with antisera specific for rat mu-chain indicates that IgM and possibly early IgG-secreting PFC have mu heavy chains on their surface. These data suggest that the PFC membrane is progressively changing during the maturation of the antibody response.