B-lymphocyte populations in Xenopus laevis.

Two-color immunofluorescence technique was used to show the development and distribution of surface mu- cytoplasmic mu+ (s mu- c mu+) pre-B, s mu+ B- and s mu+ cIg+ plasma cells in metamorphic, postmetamorphic, and adult Xenopus. Generation of pre-B cells was evident in hematopoietic liver and spleen, but not in bone marrow, thymus, and duodenal mucosa. Surface immunoglobulin positive small lymphocytes were the most abundant in the spleen while plasma cells were detected in the thymus, duodenal mucosa, spleen, and liver.

Tryptic digestion of Xenopus IgM and IgY molecules.

Xenopus IgM and IgY molecules were digested by trypsin. Their respective fragments were separated by gel filtration and immunoadsorption. The purified fragments were characterized by SDS-PAGE and immunoblotting.

Immunoglobulin Fc receptor molecules on Xenopus laevis splenocytes.

The existence of membrane-associated Fc receptors for IgY (Fc nu R) or IgM (Fc mu R) was demonstrated on a large percentage of Xenopus splenocytes. The Fc receptors were detected by direct fluorescent staining in which the spleen cells were incubated with fluorescein isothiocyanate (FITC)-conjugated antigen-complexed IgY antibodies or with FITC-conjugated heat-aggregated IgM. Results showed that 28.

Partial characterization of different cell types found in the Xenopus laevis lymphoreticular tumor based on the presence or absence of surface immunoglobulins and Fc molecules.

Cells of Xenopus laevis lymphoreticular tumor induced by tumor tissue transplantation were examined for surface Ig and Fc receptor molecules in order to evaluate the different cell types found in the tumor. Direct immunofluorescent technique, using fluorochrome conjugated rabbit antisera to Xenopus Ig's, detected Ig molecules on the surface of a mean of 31.7 +/- 11.

Anti-immunoglobulin M induces both B-lymphocyte proliferation and differentiation in Xenopus laevis.

Anti-IgM induced the proliferation of spleen lymphocytes of the amphibian Xenopus laevis as determined by 3H-thymidine uptake. The responding cells were B lymphocytes, since lymphocyte populations enriched in surface-Ig-positive cells exhibited an increased proliferative response, and spleen cells from larvally thymectomized animals still responded to anti-IgM. Immunofluorescence analysis and gel electrophoresis of biosynthetically labeled Ig polypeptides revealed that lymphoblasts induced by anti-IgM differentiated into plasmablasts that synthesized and secreted mainly IgM and small amounts of IgY.

Mitogen-induced B-cell differentiation in Xenopus laevis.

Spleen cells from the South African clawed toad Xenopus laevis proliferate vigorously upon pokeweed mitogen (PWM) stimulation, as measured by 3H-thymidine uptake. The peak response is observed after 6-8 days of culture, and both light- and electron-microscopy examinations of stimulated cells reveal the presence of a large number of lymphoblasts. Beside proliferation, PWM induces the in vitro differentiation of a large proportion of lymphoblasts into immunoglobulin (Ig)-producing plasmablasts, as shown by direct immunofluorescence.

Biochemical studies of Xenopus laevis lymphocytes surface immunoglobulins.

Cell surface immunoglobulins of adult Xenopus laevis splenic small lymphocytes were analysed utilizing direct immunofluorescent staining and lactoperoxidase-catalysed radioiodination followed by immunoprecipitation of Ig molecules and characterization on SDS-PAGE. Nearly 30% of splenic lymphocytes are surface Ig positive. The HMW and LMW Ig classes are present on the surface of 23% and less than 5% of the cells, respectively.

Immunoglobulin evolution: chemical study of clawed toad (Xenopus laevis) heavy and light chains.

NH2 terminal amino acid sequence determinations of clawed toad (Xenopus laevis) immunoglobulins indicate that approximately 30% of the heavy chains and less than 5% of the light chains have unblocked NH2 termini. The major amino acid sequence of the X. laevis 7S immunoglobulin heavy chains is the same as that of the 19S immunoglobulin heavy chains.

Xenopus laevis 19S immunoglobulin. Ultrastructure and J chain isolation.

Electron microscopy examination of the 19S immunoglobulin of Xenopus laevis revealed a hexameric structure with a central core. The molecules measured 360-430 A across the span of the arms and the average diameter of the central region was 140 A. A polypeptide, homologous to human J chain, was isolated by chromatography on DEAE-cellulose from the reduced and alkylated X.

Studies on immunoglobulins of Xenopus borealis, Xenopus clivii and Xenopus muelleri.

Following immunization with human IgG three species of anuran amphibians, Xenopus borealis, Xenopus clivii and Xenopus muelleri, were found to synthesize two molecular populations of antibodies associated with 19S and 7S fractions of the sera. These antibodies, designated high (HMW) and low (LMW) molecular weight immunoglobulins, were isolated and their constituent heavy (H) and light (L) polypeptide chains separated following extensive reduction and alkylation in a relative yield of about 70% and 30% respectively. The molecular weights of H and L chains of the three species were determined by SDS-acrylamide gel electrophoresis.

Structural studies of the Xenopus 19S immunoglobulin and 7S immunoglobulin and two immunoglobulin-like proteins.

Xenopus laevis 19S and 7S immunoglobulins (Ig) were extensively reduced and alkylated, their H and L chains spearated and their molecular weights determined. Two kinds of L chains of molecular weight 25,000 and 27,000 were revealed by SDS-polyacrylamide gel electrophoresis. In addition two Ig-like proteins consisting of heavy chains only, of 19S H-type and with similar molecular weight, were detected in Xenopus serum ans isolated.

Studies on Xenopus laevis immunoglobulins.

The anuran amphibian has been shown to produce two classes of antibodies to HGG, BSA and Hc. These antibodies were characterized by gel filtration on Sephadex G-200 as `19S' and `7S' immunoglobulins. In the course of immunization, antibody activity could be initially detected in the `19S' immunoglobulin fraction, followed by the appearance of the activity in the `7S' immunoglobulin fraction at a later stage of immunization.