Structure of MHC class I and class II cDNAs and possible immunodeficiency linked to class II expression in the Mexican axolotl

Despite the fact that the axolotl (Ambystoma spp. a urodele amphibian) displays a large T-cell repertoire and a reasonable B-cell repertoire, its humoral immune response is slow (60 days), non-anamnestic, with a unique IgM class. The cytotoxic immune response is slow as well (21 days) with poor mixed lymphocyte reaction stimulation. Therefore, this amphibian can be considered as immunodeficient. The reason for this subdued immune response could be an altered antigenic presentation by major histocompatibility complex (MHC) molecules. This article summarizes our work on axolotl MHC genes. Class I genes have been characterized and the cDNA sequences show a good conservation of non-polymorphic …

Natural and induced apoptosis during lymphocyte development in the axolotl

Lymphocytes apoptosis was characterized in a urodele amphibian, the axolotl, by morphology using electron microscopy and by flow cytometry after propidium iodide staining, as well as by biochemical criteria with the detection of DNA ladders after glucocorticoid treatment. The morphological and biochemical features observed in treated axolotls are in accordance with the criteria of apoptosis found in different models of mammalian lymphocyte programmed cell death. The onset of natural apoptosis was then detected by DNA fragmentation in thymus and in spleen during lymphocyte development and ontogenesis. A typical DNA ladder characteristic of apoptosis is detectable in the thymus as early as 5 …

Axolotl MHC architecture and polymorphism.

The MHC of the urodele amphibian Ambystoma mexicanum consists of multiple polymorphic class I loci linked, so far as yet known, to a single class II B locus. This architecture is very different from that of the anuran amphibian Xenopus. The number of class I loci in the axolotl can vary from 6 to 21 according to the haplotypes as shown by cDNA analysis and Southern blot studies in families. These loci can be classified into seven sequence groups with features ranging from the class Ia to the class Ib type. All individuals express genes from at least three of the seven groups, and all individuals possess the class Ia-like type.

Amphibian Immune System

Axolotl MHC class II β chain: predominance of one allele and alternative splicing of the β1 domain

The axolotl MHC is composed of multiple polymorphic class I loci linked to class II B loci. In this report, evidence of the existence of one class II B locus (Amme-DAB) that codes for two different transcripts is given. A 2.1-kb transcript is translated to a complete β chain and a shorter transcript of 1.8 kb encodes a molecule lacking the β1 domain. For two complete class II B mRNA synthesized, up to one mRNA devoid of the β1 domain is synthesized. Alternative splicing involving a peptide binding domain at a class II B locus evidenced in axolotl (Ambystoma mexicanum) is also observed for A. trigrinum, the tiger salamander. Very little variability is found among various axolotl MHC class II…

Isolation of Mhc class I cDNAs from the axolotl Ambystoma mexicanum.

Class I major histocompatibility complex (Mhc) cDNA clones were isolated from axolotl mRNA by polymerase chain reaction (PCR) and by screening a cDNA phage library. The nucleotide and predicted amino acid sequences show definite similarities to the Mhc class Ialpha molecules of higher vertebrates. Most of the amino acids in the peptide binding region that dock peptides at their N and C termini in mammals are conserved. Several amino acids considered to be important for the interaction of beta2-microglobulin with the Mhc alpha chain are also conserved in the axolotl sequence. The fact that axolotl class I A cDNAs are ubiquitously expressed and highly polymorphic in the alpha1 and alpha2 doma…