Presentation des elements du systeme immunitaire de Xenopus: systeme lymphoide, systeme d'histocompatibilite majeur, immunoglobuline. Le fonctionnement de ce systeme est considere (reponse immune, tolerance, diversite des anticorps) ainsi que son developpement. L'impact de la polyploidie sur le systeme immunitaire de Xenopus est discute

The immune system of xenopus

One-way and two-way mixed leukocyte reactions (MLR) have been performed using cells isolated from peripheral blood of chickens from four different inbred lines (CA, CB, WA and WB).



MLR between chickens from the same line, or from lines CA and CB (which have the same major histocompatibility antigens (B antigens)) were always negative; MLR between chickens from lines differing at the B locus were always positive, even when the lines compared (WA, WB) had otherwise identical or very similar genetic backgrounds. This evidence that a locus or loci controlling the MLR is linked to the major histocompatibility locus in the chicken was confirmed by the results of MLR performed with leukocytes from the F2 progeny of a WA × CB cross. These experiments also exclude (at least for the WA/CB combination) the role in the reaction of other, non-B-linked MLR loci.



The evolution of the vertebrate major histocompatibility complex is discussed in the light of these findings.

The mixed leukocyte reaction in chickens. Evidence for control by the major histocompatibility complex.

Genetic aspects of tolerance to allografts induced at metamorphosis in the toadXenopus laevis were studied in one sibship expressing four different major histocompatibility complex (MHC) haplotypes. Tolerance by skin grafting was induced during metamorphosis in thiourea-blocked individuals, a technique that allows prolonged observation of graft behavior at this stage. Four classes of mutually tolerant animals could be determined. The use of antisera recognizing red blood cell antigens segregating with mixed lymphocyte reaction (MLR) haplotypes revealed that the four abovementioned classes corresponded to the four MHC genotypes of the family. The tolerance is, therefore, preferentially induced to antigens not dependent on the MHC. Under certain circumstances tolerance can also be induced to MHC antigens, provided that the animals differ at the level of one MHC haplotype only. Study of MLR during ontogeny suggested that, between sibs, only the two MLR haplotype differences were stimulatory at metamorphosis, whereas in larval and adult animals a one-haplotype difference was enough for stimulation.

Genetic aspects of the tolerance to allografts induced at metamorphosis in the toadXenopus laevis

The genetic control of the collaboration between Xenopus T and B cells has been analyzed in vitro using cells from five strains of major histocompatibility complex-defined Xenopus.



When carrier (fowl gamma-globulin)-primed T cells and hapten (dinitrophenylated keyhole limpet hemocyanin)-primed B cells differed by minor histocompatiblity antigens or by only one haplotype of the major histocompatibility complex, the collaboration was efficient in the sense that large numbers of plaques, low-molecular weight antibodies and high-affinity IgM antibodies could be recorded in the cultures challenged with dinitrophenylated fowl gamma-globulin. However, when T and B cells differed at both alleles of the major histocompatibility complex, lower numbers of plaques were obtained, no low-molecular weight anti-hapten antibodies could be detected, and the IgM antibodies that were sometimes synthesized were of low affinity. This suggests that the major histocompatibility complex, or a gene linked with it, affects the collaboration between Xenopus T and B cells in a way perhaps similar to that described in mammals.

Genetic control of T helper cell function in the clawed toad Xenopus laevis.

Family studies inXenopus laevis (2n=36 chromosomes) demonstrate the expression of a single major histocompatibility complex in this species. Mixed leukocyte studies in two families ofXenopus vestitus (2n=72 chromosomes) indicated that this reaction was also under the control of a single genetic region. These studies suggest that, in this polyploid species, the switch from tetrasomic to disomic inheritance has already been accomplished for this locus. In contrast, segregation of mixed leukocyte reaction determinants and patterns of graft rejection in two families ofXenopus ruwenzoriensis (2n=108 chromosomes) were incompatible with the expression of a single major histocompatibility complex, and suggest that polysomic inheritance of this locus is maintained in this species. This interpretation was confirmed by the finding in a sibship of hybrids betweenXenopus ruwenzoriensis andXenopus laevis (2n=54+18) of more than four classes of mixed leukocyte reaction-identical sibs. In laboratory-created triploid animals (trispecies hybrid amongXenopus laevis, Xenopus gilli, andXenopus clivii), mixed leukocyte reaction and grafting experiments demonstrated that the major histocompatibility complex of each constituting species was codominantly expressed.

Miggiano Vc

Papers

The mixed leukocyte reaction in the toad Xenopus laevis: a family study.