Autoimmunity as a possible limiting selection pressure for the individual MHC IIB allele diversity in the three-spined stickleback Gasterosteus aculeatus?
Year: 2011
Type: other
Abstract: Genetic diversity is a prerequisite for evolution. The genes of the Major Histocompatibility\nComplex (MHC) show genetic variation. They are polygenic and contain highly polymorphic\nloci. MHC molecules are an important part of the adaptive immune system due to their ability\nto bind and present different antigens to the T-lymphocytes. But this high specificity also\nimplies a risk: the higher the number of recognized antigens, the more likely the similarity of\nforeign and auto antigens. This can cause a loss of self tolerance mechanisms due to cross\nreactions during molecular mimicry. The MHC might be a key molecule for selection,\nadaptive processes and speciation.\nGasterosteus aculeatus shows an intermediate number of MHC IIB alleles. On the one hand,\ntoo few different MHC IIB alleles demonstrate an insufficient diversity to detect a large\nnumber of parasite antigens. But on the other hand, there must be a limiting selection\npressure, which causes this intermediate optimum of MHC IIB alleles. A possible\ndisadvantage assumes that too many alleles might lead to self-immunoreactivity. Therefore,\nthis thesis focuses on a possible correlation between certain immunological changes, which\nmight be associated with autoimmune reactions, and the individual MHC IIB allele diversity of\nthe three-spined stickleback. It is a pilot study about auto aggressive reactions as a possible\nlimiting selection pressure on the evolution of the MHC IIB allele diversity. Thus, I used\ndifferent methods to examine different aspects of this topic.\nFirst, the MHC class IIB allele configuration of parental fish of 14 different families was\ndetermined. The results indicate five families, whose offspring showed a MHC class IIB allele\ndiversity of either two or four different alleles. The MHC genotyping of parents and offspring\nwas done via the Reference Strand-mediated Conformation Analysis (RSCA). The next step\nwas the isolation of several inflammatory genes. Different primer combinations were tested\nvia standard PCR and Agarose gelelectrophoresis. After that, primer specificity was checked\nvia direct sequencing and quantitative Real Time PCR.\nI was able to isolate IL 1 beta, MIF, IgM and MHC II in the genome of Gasterosteus\naculeatus. After that, head kidney, spleen, liver, kidney, gut, gonads, heart and brain were\ndissected and blood was taken from the caudal vein. The total immunoglobulin level of the\nplasma was measured with the help of an Enzyme-linked immunosorbent assay (ELISA).\nRNA of head kidney, gut, kidney and spleen was isolated and reverse transcribed into cDNA.\nThe expression levels of the established inflammatory genes MIF, IL 1 beta, IgM and MHC\nclass II were measured, relative to those of the housekeeping genes L13 and Ubiquitin. This\nwas done via the quantitative Real Time PCR, based on the non-specific reporter molecule\nSYBR Green I. The raw gene expression data was normalized with the software qBase Plus\nand a permutational multivariate analysis of variance was performed with the help of the\nsoftware R 2.11.1.\nThe results indicate the family of origin and sex as influencing factors. The influence of the\ndissection day is due to an artefact. Maybe different families contain different repertoires of\nimmunological factors. This might be due to differences in their genetic background. In\nhumans, it has been assumed that autoimmunity is correlated with female sex hormones.\nTherefore, it might be possible that female sex hormones of teleost fish are correlated with\nthe occurrence of autoimmune diseases. It would be interesting to examine, whether and\nhow female sex hormones can influence the adaptive immune system.\nDue to a low p-value (p = 0.074), it might be possible that the number of MHC IIB alleles also\naffects certain immunological parameters. Therefore, it might be interesting to breed fish with\nvery high and low numbers of MHC IIB alleles and to expose them to many parasites and\nmany different types of parasites. Maybe the costs, namely the occurrence of auto\naggressive reactions, are lower than the benefits, namely a high resistance towards\nparasites. It might be possible that there is a trade-off between the resistance towards\nparasites and auto aggressive reactions\nThe results of the expression assay indicate that IL 1 beta seems to be an important\ncomponent of the adaptive immune response in Gasterosteus aculeatus. It shows a higher\nexpression in the head kidney of individuals with four MHC IIB alleles. Apart from that, a\npositive correlation of IL 1 beta- and MHC II expression is observed in head kidney, spleen\nand kidney. It might also be helpful to detect more possible inflammatory genes for a better\nunderstanding of the complex network of associations between several cytokines of the\nadaptive immune system. Some studies about cytokines in teleost fish include stimulations of\nthe adaptive immune system with LPS, FCA and ATH. They resulted in an increase of\nexpression levels in several organs. Therefore, another interesting project might deal with the\nartificial induction of autoimmune reactions due to stimulation of the immune system of\nGasterosteus aculeatus.
Source: MPG.PuRe (Max Planck Society)
Authors: Anja Krause, Manfred Milinski, Hinrich Schulenburg
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W761710204