Exposed epitopes on a Trypanosoma equiperdum variant surface glycoprotein altered by point mutations.

African trypanosomes are covered by a dense protein layer that is immunologically distinct on different trypanosome isolates and is termed the variant surface glycoprotein (VSG). The different VSGs are expressed in a general order, where some VSGs appear preferentially early in infection and others only later. The exposed epitopes on a late antigen, VSG 78, of T.equiperdum were studied by the technique of monoclonal antibody (MAb) escape selection. MAbs that neutralize trypanosomes bearing VSG 78 reacted with the VSG only when it was attached to the trypanosome surface, suggesting that the most immunogenic surface epitopes are conformational. Trypanosome clones resistant to one of the MAbs yet still expressing VSG 78 or 78(20) were isolated in vitro. Two independent variants resistant to MAb H3 changed Ser192 to Arg by a single base change in the VSG gene and a variant resistant to MAb H21 had a single base change that converted Gln172 to Glu. A variant resistant to MAb H7 had several changes in the VSG gene, a gene conversion in the 5' region and an isolated mutation in codon 220 that is proposed to be responsible for the resistance phenotype. The isotypic bias of the MAbs against VSG 78 and an analysis of the natural variants that are resistant to MAb 78H21 suggest that glycosylation plays a role in the immunogenicity of these proteins. The analysis defines some of the exposed amino acid residues and demonstrates that VSG genes are altered by mutations and small gene conversions as well as replaced by large gene conversion-like events. The results provide biological data supporting the model of VSG structure obtained by crystallographic studies.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Anticomplement actions of heparin-like and protamine-like substances]

A reciprocal inhibition exist in vitro between the anticomplementary activity of protamine and heparin like substances. The concentration required for inhibition is approximately of the same order for the both groups of substances.     

Effects of cortisol on serially propogated fibroblast cell cultures derived from the rabbit retal lung and skin.

Cortisol affects the growth of serially propogated, fibroblast cell cultures derived from the rabbit fetal lung in a manner which is dependent upon the gestational age of the material used: early in gestation (20 days), the hormone (10(-7)-10(-5) M) stimulates [6-3H]thymidine incorporation into DNA, while in late gestation (28 days), cortisol (10(-7) and 10(-6) M) inhibits this process. Cultures derived from the rabbit fetal skin are inhibited by cortisol (10(-5) M) at both gestational ages. Fibroblasts derived from lung, but not from skin, efficiently convert cortisone to cortisol and this activity increases with advancing gestation. Cortisol does not affect the incorporation of [3H]choline into lecithin by confluent cultures of any of the fibroblast types studied.     

Les substances a fonction sulfhydrile du protoplasma

Sans résumé     

What can we learn from noncoding regions of similarity between genomes?

Background  

In addition to known protein-coding genes, large amounts of apparently non-coding sequence are conserved between the human and mouse genomes. It seems reasonable to assume that these conserved regions are more likely to contain functional elements than less-conserved portions of the genome.     

Nitric oxide inhibits spleen cell proliferative response after burn injury by inducing cytostasis,apoptosis, and necrosis of activated T lymphocytes: role of the guanylate cyclase

We previously showed that an overproduction of nitric oxide (NO) by macrophages was responsible for the collapse of lymphoproliferative responses after burn injury in rats. First, we demonstrate here that 10 days post-burn, the inhibition of splenocyte response to concanavalin-A results from cytostatic, apoptotic, and necrotic effects of NO on activated T cells. This was evidenced by various criteria at the levels of DNA, mitochondria, and plasma membrane. Inhibition of NO synthase by S-methylisothiourea (10 microM) normalized all the parameters. Second, we show that two soluble guanylate cyclase (sGC) inhibitors, LY83583 and ODQ, restored the proliferative response in a concentration-dependent manner. LY83583 (0.5 microM) rescued T cells from apoptosis. Similar results were obtained with KT5823 (5 microM) a specific inhibitor of protein kinase G (PKG). In contrast, neither LY83583 nor KT5823 inhibited NO-induced necrosis. These results suggest that NO blocked T cells in the G1 phase and induced apoptosis through a sGC-PKG-dependent pathway and necrosis through an independent one.