Immunoglobulin isoantigens (allotypes) in the mouse

Murine antisera raised against allogeneic lymphoid cells often contain antibodies to IgM allotypes. Rarely, allotypic antibodies to IgM have been found after immunization withB. pertussis anti-B. pertussis conjugates. Using both types of antibodies, we have defined a new constant-region locus for both secreted and membrane-bound chains. This locus,Ig-6, is closely linked to the previously described H-chain constant-region loci (Ig-1 throughIg-5) and is subject to allelic exclusion. We have identified three alleles and four antigenic specificities ofIg-6.Authors listed alphabetically     

Vitamin D metabolism and expression in rats fed on low-calcium and low-phosphorus diets

1. Cholecalciferol, radioactively labelled with both (14)C and (3)H, was administered weekly for 7 weeks to rats that had been depleted of vitamin D for 4 weeks before repletion with the radioactive vitamin. This permitted measurement of the steady-state effect on vitamin D metabolism of low-calcium and low-phosphorus regimens, as compared with a normal mineral intake. These dietary manoeuvres were carried out during the last 3 weeks of repletion. Cholecalciferol, 25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol were determined in plasma, intestine, kidney and bone. Ca(2+)-binding-protein content was measured in intestine and kidneys of comparable animals. 2. In rats on the low-calcium diets, 1,25-dihydroxycholecalciferol concentration was elevated in plasma, bone, kidney and intestine, and intestinal Ca(2+)-binding protein was increased to over twice the concentration found in the control animals. 3. The low-phosphorus regimens led to a decrease in plasma phosphate and 1,25-dihydroxycholecalciferol in all tissues studied, for the latter to the point where it was undetectable in plasma and bone. Intestinal and renal concentrations of Ca(2+)-binding protein were unchanged in the low-phosphate-intake group and decreased in the very-low-phosphate-intake group. 4. It is concluded that in the rat, unlike in the chick, hypophosphataemia is not associated with a stimulation of the production of 1,25-dihydroxycholecalciferol or its expression in the synthesis of Ca(2+)-binding protein. Therefore the plasma phosphate concentration does not appear to be directly involved in the regulation of the functional metabolism of vitamin D.     

Adherent cells in tumor immunity

The present studies explored the role of adherent cells in tumor immunity. Lymph node cells from mice bearing large tumors appeared to be maximally stimulated in vivo and incapable of further stimulation by cells of the same tumor in vitro. Removal of the adherent cell population resulted in a marked decrease in the spontaneous background activity of the remaining nonadherent cells and allowed these cells to undergo stimulation when cultured in the presence of mitomycin-blocked tumor cells. The role of the adherent cell in the maintenance of a state of continuous stimulation was further elucidated by experiments in which lymph node cell populations were reconstituted from the adherent and nonadherent subpopulations. It was also shown that adherent lymphoid cells from tumor-bearing mice, but not from normal mice, were capable of stimulating tumor-immune lymphocytes in a manner similar to intact mitomycin-blocked tumor cells.     

Characterization of tetanus toxins and toxin components by amino terminal analyses

Extract tetanus toxin, filtrate tetanus toxin, and the heavy and light chains of filtrate toxin were analyzed for their amino termini with 4-N,N-dimethylaminoazobenzene-4′isothiocyanate and phenylisothiocyanate. Extract toxin (intracellular toxin) is a single-chain polypeptide with proline as the amino terminus. Filtrate toxin (extracellular toxin) is a mixture of species produced by endogenous proteases, and showed three major amino terminal residues, proline, asparagine, and serine. Cleavage points in the filtrate toxin molecule appear to be on either side of a disulfide bond. Reductive and nonreductive preparative electrophoresis of filtrate toxin produce different species of light and heavy chains. The light chains have a single amino terminus of proline, indicating that the light chain is the amino terminal portion of the toxin molecule. The heavy chains showed no proline but rather asparagine and serine as the major amino termini. Small amounts of other amino terminal residues were present, indicating microheterogenity at the cleavage sites in the toxin. The results permit the construction of a model of tetanus toxin which is consistent with the fragments obtained from either reductive or nonreductive preparative electrophoresis of filtrate toxin.     

Amino group modification inhibits ristocetin cofactor activity of human von Willebrand factor

Purified von Willebrand factor rapidly loses activity when treated under mild conditions with the highly specific amino group reagent trinitrobenzenesulfonic acid. Greater than 90 percent inhibition of activity is achieved by modification of only 7 percent of the amino groups. Other modifications such as acetylation and succinylation also abolish activity. It is unlikely that the essential rapidly reacting amino groups function simply in an electrostatic manner since modifications such as amidination and methylation which produce derivatives which retain positive charge are also inactive or nearly so.     

The genetics of phenotypic plasticity. IV. Chromosomal localization

The contributions of each chromosome to the traits thorax size and plasticity of thorax size as affected by temperature in Drosophila melanogaster were measured. A composite stock was created from lines previously subjected to selection on thorax size or plasticity of thorax size. A chromosome extraction was performed against a uniform background lacking genetic variation, provided by a stock of marked balancer flies. With regard to amount of plasticity, chromosome I and the balancer stock showed no plasticity, the composite stock showed the greatest plasticity, and chromosomes II and III were intermediate. Chromosome I showed significant genetic variation for thorax size at both 19° C and 25° C, but not for plasticity, while chromosome II showed significant genetic variation for plasticity, but not for thorax size. Chromosome III showed significant genetic variation for both thorax size and plasticity. We tested the predictions of three models of the genetic basis of phenotypic plasticity: overdominance, pleiotropy, and epistasis. The results support the epistasis model, in agreement with earlier work. The amount of developmental noise was correlated with phenotypic plasticity at 25° C, in agreement with earlier work. A negative correlation was found at 19° C for chromosome II, contrary to earlier work.     

Early induction of ribonucleotide reductase gene expression by transforming growth factor beta 1 in malignant H-ras transformed cell lines.

Previous investigations have indicated that the suppression of proliferation by transforming growth factor (TGF) beta 1 is often lost upon cellular transformation, and that proliferation of some tumors is stimulated by TGF-beta. The present study provides the first observation of a link between TGF-beta 1 regulation of this process and alterations in the expression of ribonucleotide reductase, a highly controlled rate-limiting step in DNA synthesis. A series of radiation and T24-H-ras-transformed mouse 10T1/2 cell lines exhibiting increasing malignant potential was evaluated for TGF-beta 1 induced alterations in ribonucleotide reductase M1 and M2 gene expression. Early increases in M1 and/or M2 message and protein levels were observed only in malignant cell lines. The TGF-beta 1 induced changes in M1 and/or M2 gene expression occurred prior to any detectable changes in the rates of DNA synthesis, supporting the novel concept that ribonucleotide reductase gene expression can be elevated by TGF-beta 1 without altering the proportion of cells in S phase. T24-H-ras-transformed 10T1/2 cells were transfected with a plasmid containing the coding region of TGF-beta 1 under the control of a zinc-sensitive metallothionein promoter. When these cells were cultured in the presence of zinc, a large induction of TGF-beta 1 message was observed within 1 h. Both M1 and M2 genes were also induced, with increased mRNA levels appearing 2 h after zinc treatment, or 1 h after TGF-beta 1 message levels were clearly elevated. In total, the data suggests a mechanism of autocrine stimulation of malignant cells by TGF-beta 1, in which early alterations in the regulation of ribonucleotide reductase may play an important role.     

Delineation of type-specific regions on the envelope glycoproteins of human T cell leukemia viruses.

Two different approaches were used to map the type-specific regions on human T cell leukemia virus (HTLV) envelope glycoproteins. 1) Antibody reactivities of polymerase chain reaction-confirmed HTLV-I or HTLV-II carriers' sera were analyzed by Western blot assay with seven recombinant proteins containing different regions of HTLV-I or HTLV-II envelope proteins. 2) Rabbit antibodies elicited by nine HTLV-I Env synthetic peptides were used to react with the native HTLV envelope glycoproteins in an antibody-dependent cellular cytotoxicity (ADCC) assay. The results of the Western blot analysis showed that RP-B2, which contains amino acid residues 166 to 213 from HTLV-II exterior glycoprotein, was specifically reactive with 90.6% (48 of 53) of the HTLV-II carriers' sera but not with any of the HTLV-I carriers' serum (0 of 71). In contrast, RP-B, which contains amino acid residues 166 to 229 from HTLV-I exterior glycoprotein, was reactive with 85.1% (114 of 134) of the HTLV-I carriers' sera but not with any HTLV-II carrier serum (0 of 62). Furthermore, anti-HTLV-I Env synthetic peptide antibody-mediated ADCC identified several distinguishing HTLV-I ADCC epitopes in the middle region (amino acid residues 177 to 257) of the HTLV-I exterior glycoprotein. Therefore, HTLV type-specific epitopes reside mainly in a 69-amino acid sequence bounded by two cysteine residues (amino acids 157 and 225 for HTLV-I and 153 and 221 for HTLV-II), in the middle region of the exterior envelope glycoproteins.     

Ultrastructural specialization of intestinal epithelium over Peyer's patches in the bonnet monkey, Macaca radiata.

The follicle associated epithelium (FAE) which separates the lymphoid follicle of Peyer's patch from the gut lumen is known to have specialized cells called M cells or "microfold" cells in man and certain animals. These cells are considered to be involved in antigen uptake and transport. Our light microscopic study of the small intestine of bonnet monkeys suggested the presence of such specialised cells in FAE. We have confirmed the presence of M cells in bonnet monkey FAE having ultrastructural features very similar to those of human M cells.     

The influence of nearest neighbors on the rate and pattern of spontaneous point mutations

Summary The numbers and local sequence environments of the two types of substitution mutation plus additions and deletions have been obtained directly in this study from differences between a large number of extant primate gene and pseudogene sequences. A total of 3786 mutations were scored in regions where similarities between pseudogene and corresponding gene sequences is 85%, comprising 30% of the pseudogene database of 80,584 bp. The pattern of mutations obtained in this fashion is almost identical to that obtained by Li et al. (1984) using a slightly different, more direct approach and with a smaller database. When mutations were scored, the neighbor pairs on the 5 and 3 sides were also noted, leading to a large 16 × 12 matrix of transitions and transversions. Biases of varying magnitude are found in the rates of substitution of the same base pair in different local sequence environments. The overall order for the effect of the 5 neighbor on the rates of substitution mutation of a pyrimidine is A > C T > G, and G > A > T > C for the 3 neighbor; where these results represent the average of substitution rates for the complement purine with complement neighbors of bases ordered above. The order for the 3 neighbor is essentially the same for the two transitions and most of the four transversions as well; however, the order for the 5 neighbor is more variable. The overall rate for the C · G T · A transition is not unusual, however the presence of a 3 neighboring G · C pair boosts the rate substantially, presumably due to specific cytosine methylation of the CG doublet in primate DNAs. The rate of the T · A C · G transition is also well above average when the 3 neighbor is an A · T, and to a lesser extent a G · C, pair. The latter bias is typical in that it reflects the association of alternating pyrimidine-purine sequences with increasing mutation rates. The substitution of the pyrimidine in a 5 purine-pyrimi-dine-purine3 sequence generally occurs much faster than in a pyrimidine tract and points to the local conformation as a major determining factor of the substitution rate. An apparent inverse relationship is found between starting and product doublet frequencies of base pairs undergoing mutations with specific 3 neighbors, indicating that differences in intrinsic substitution rates of base pairs with specific neighbors are a key factor in producing the familiar biases of nearest-neighbor frequencies.Offprint requests to: R. D. Blake