REGULATION OF INTERLEUKIN-13 RECEPTOR CONSTITUENTS ON MATURE HUMAN B-LYMPHOCYTES

Human B cells stimulated through both their immunoglobulin and CD40 re ceptors up-regulate 745 +/- 51 interleukin (IL)-13 ligand binding site s with an affinity of 0.91 +/- 0.08 nar within 24 h. IL-13 binds prima rily to the IL-13R alpha 1 with subsequent sequestration of the IL-4R alpha into the complex. IL-13R alpha 1 may also be found in those rece ptors capable of binding IL-4. gamma chain (gamma(c)) participates in receptors capable of binding IL-4 but is not found in association with bound IL-13, Dimeric receptors composed of the IL-4R alpha complexed with either the IL-13R alpha 1 or gamma(c) occur simultaneously within defined B cell populations. mRNAs for all receptor constituents are i ncreased subsequent to immunoglobulin stimulation alone, while maximal expression of IL-13R alpha 1 is more dependent upon co-stimulation of immunoglobulin and CD40 receptors, mRNA levels for IL-13R alpha 1 var y over a wider range subsequent to surface stimulation than other rece ptor components. Although gamma(c) is not bound to IL-13 in B cells un der the conditions evaluated, it may influence IL-13 binding by compet ing with IL-13R alpha 1 for association/sequestration with the IL-4R a lpha chain, IL-13R alpha 2 does not participate in the IL-13 receptor that is up-regulated upon activation of quiescent tonsillar B lymphocy tes, although mRNA for the protein may be found in the centroblastic f raction of tonsillar cells.