title: Antigen-induced acceleration of shedding and replacement of B cell antigen receptors requires mature T cells.
abstract: To determine which early and intermediate events in the response of antigen-binding B cells to a T-dependent antigen (sheep erythrocytes [SRC]) require T help, the antigen-induced changes in receptor turnover and surface IgD loss in BALB/c athymic nu/nu mice were compared with that of nu/+ littermates and +/+ BALB/c mice. Nonimmune SRC antigen-binding spleen B cells (ABC) from +/+, nu/+, and nu/nu BALB/c mice coexpressed IgM and IgD, and 85 to 95% retained receptors well when incubated for 2.5 hr in 100 micrograms/ml cycloheximide (which prevents receptor replacement). Also they were able to regain their ability to bind antigen by 18 hr after pronase treatment, but not by 2 hr. However, 5 days after in vivo immunization, 1) the proportion of ABC expressing surface IgD declined from around 90% to less than 50% in +/+ mice and nu/+ mice but not in nu/nu mice; 2) substantial recovery of antigen-binding occurred by 2 hr after pronase treatment in +/+ and nu/+ ABC but not in nu/nu ABC; and 3) when spleen cells were incubated in cycloheximide, uncompensated receptor shedding reduced +/+ and nu/+ ABC by around 80% but produced only about a 10% reduction in nu/nu ABC. Thus, although the ABC in nonimmune nu/nu mice appeared normal with respect to their surface Ig turnover and expression, they failed to undergo the normal antigen-induced loss of IgD or acceleration of surface Ig shedding and replacement, suggesting that these intermediate activation events require interaction with mature T cells. To determine whether this interaction had to occur during B cell development, during the development of the immune response, or during receptor shedding or replacement itself, cell transfer experiments were carried our wherein nu/+ T cells were transferred i.v. to nu/nu littermates 1 day before immunization with SRC. In the transfer recipients, pronase-treated day 5 ABC were then able to replace and shed their receptors at the accelerated rate, like ABC from +/+ and nu/+ mice. In contrast, the co-incubation of 5-day immune nu/+ T cells with nu/nu B cells did not alter the rate of shedding or replacement.
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D001789:Blood Group Antigens; D005260:Female; D006133:Growth Substances / Q000502:physiology; D007072:Immunoglobulin D / Q000096:biosynthesis; D015847:Interleukin-4; D008222:Lymphokines / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D011947:Receptors, Antigen, B-Cell / Q000096:biosynthesis*; D012756:Sheep; D013601:T-Lymphocytes / Q000276:immunology* / Q000502:physiology
chemical_list: D001789:Blood Group Antigens; D006133:Growth Substances; D007072:Immunoglobulin D; D008222:Lymphokines; D011947:Receptors, Antigen, B-Cell; D015847:Interleukin-4