Somatic translocation and differential expression of Ig mu transgene copies implicate a role for the Igh locus in memory B cell development.

Memory B cells of mice with Ig mu transgenes often carry transgene copies that have moved into the Igh locus via somatic translocation. This phenomenon has been attributed to a selection pressure for somatic hypermutations, which generally are observed at much higher frequencies in translocated copies than in ectopic copies. We tested this idea by immunizing Ig-mu transgenic mice in a manner designed to select B cells that required only one V(H) mutation for a switch in antigenic specificity and recruitment into the memory pool. Despite the minimal mutation requirement, hybridomas carrying somatic translocations to the Igh locus were obtained. Importantly, this occurred despite the fact that translocated and untranslocated mu-transgenes were mutated comparably. Evidently, a strong selection advantage was conferred upon B cells by the somatic translocations. Among the hybridomas, translocated mu-transgenes were active, while ectopic mu-transgenes were uniformly silent. The translocated copy that had conferred an affinity-based selection advantage was expressed at the highest level. Moreover, translocated copies were differentially expressed among hybridoma members, which belonged to a common post-mutational lineage. This suggests that adjustments in transgene expression levels had occurred during memory cell development. These results indicate that, apart from their potential influences on somatic hypermutagenesis and class switch recombination, elements in the Igh locus promote the selection of memory B cells in another way, possibly by regulating the level of Ig expression at various stages of antigen-driven differentiation.

Characterization of antigen-binding protein in earthworms Lumbricus terrestris and Eisenia foetida.

Injection of antigen into the annelid worms Lumbricus terrestris (LT) and Eisenia foetida (EF) results in a marked increase of coelomic fluid protein concentration and the formation of a protein which binds the stimulating antigen (3). In this report we show that the increases in total protein concentration after first and second doses of antigen were higher and were achieved earlier in LT than in EF, while the accumulation of antigen-binding protein in coelomic fluid was similar in both species. Antigen-binding protein isolated by affinity chromatography retained its original binding activity. Its molecular weight in coelomic fluid as well as after isolation was 56 kD when analyzed by SDS-PAGE and immunoblotting. Under reducing conditions, two bands with mol./wt. 31 and 33 kD appeared which did not reveal detectable binding activity. This suggests that the 56 kD binding protein of annelids is composed of two disulphide-linked polypeptide chains both of which participate in antigen-binding site formation.

Lysis of inducer T cell clones by activated macrophages and macrophage-like cell lines.

We describe a sequence of reciprocal interactions between cloned inducer T cells and antigen-presenting cells (APC) that results in selective depletion of the antigen-reactive inducer cells. We show that corecognition of antigen and I-A by hapten-reactive inducer T cell clones results in (a) release of macrophage-activating factor (MAF) and other lymphokines, (b) expression of lytic activity by a subset of MAF-sensitized APC after triggering, and (3) lysis (mediated by the activated and triggered macrophage) of the inducer T cell clone and other cells in the vicinity. We suggest that this sequence of steps may limit the extent of macrophage-mediated tissue destruction by depleting the specific inducer T cell clones that initiate the response.

Structural and antigenic studies of an idiotype-bearing murine antibody to the arsonate hapten.

Mice of strain A/J responded to repeated intraperitoneal injection of Limulus hemocyanin derivatized with arsanilic acid by producing large quantities (approximately 5 mg/mL of ascites fluid) of IgG antibodies specific for this hapten. The antibodies possessed a characteristic idiotypic determinant and exhibited restricted heterogeneity as demonstrated by isoelectric focusing and primary N-terminal amino acid sequence analysis of isolated light and heavy polypeptide chains. Both light- and heavy-chain sequences were comparable to those of myeloma proteins in lack of heterogeneity. The N terminus of the light chain exhibited V KI sequence and only one position in the first 30 residues showed more than one amino acid. No variability was observed in the first 10 N-terminal residues of the heavy chain. Rabbit antiserum to the idiotype blocked binding of hapten by the purified antibody. The presence of both light- and heavy-chain antigenic determinants was required for optimal formation of the idiotypic determinant.