Effects of Major Histocompatibility Complex Under Conditionsof Species Endangerment

哺乳动物和鸟类的主要组织相容性复合体(MHC)对体液免疫和细胞免疫都有重要影响。在几乎所有被充分研究的物种中，MHC具有高度多态的特征。在随机育种群体中，大多数个体将是MHC单倍型的杂合子，因此可以受益于免疫反应基因在两种单倍型中的显性表达。另一方面，纯合子个体只能从单一单倍型的影响中受益。因此，大量多样化单倍型的持续分离将有利于野生种群的最大免疫反应能力。拟议研究的主要目标是确定在经历种群数量严重减少(濒危)的物种中，MHC单倍型纯合子个体和杂合子个体的相对适合度。由于让濒危物种的个别成员接受严格的全面免疫遗传分析是不切实际的，因此，一种种群规模不断下降的野生物种--环颈野鸡--被选为主要的实验动物。目前从鸡的12个已知的同种异体抗原系统中获得的现有知识和专业知识，应该能够在野鸡中识别相应或类似的系统，包括MHC，并在可能的范围内识别真正濒危的特别感兴趣的鸟类，如各种种类的鹤。从血型鸡群中产生的同种异体抗血清将作为血清学探针，用于鉴定其他禽类的同种异体抗原系统。随着MHC单倍型的确定，显示遗传分离的家鸡家系群体将被用于合作的生理、发育和疾病暴露研究，以调查特定单倍型在纯合和杂合个体中的特定影响。在理解MHC在小鼠和人类中的免疫功能的细胞和结构基础方面已经取得了很大进展。大量证据表明，鸡的MHC影响几个健康性状，如受精卵的孵化率、生长速度以及幼年和/或成年期的存活率。然而，到目前为止，对于MHC在野生种群中的适应功能还没有明确的了解。环颈野鸡是一种生活在野外的物种，可以很容易地用来研究MHC在生存中的作用。从所有脊椎动物物种中明显普遍存在MHC以及迄今所研究的不同物种在免疫功能上的本质相似性来看，了解MHC在野生物种适应性中的基本功能很可能对保护濒危物种的遗传规划非常重要。

The major histocompatibility complex (MHC) of mammals and birds is known to exert a major influence on both humoral and cellular immune responses. In nearly all species adequately investigated, the MHC is characterized by a high degree of polymorphism. In random breeding populations, most individuals would be heterozygous for MHC haplotypes and could thus benefit from the dominant expression of immune response genes in both of the haplotypes present. A homozygous individual, on the other hand, could benefit only from effects of the single haplotype. Thus, maximum immune response capabilities of a wild population would be favored by the continued segregation of a large number of diversified haplotypes. The primary objective of the proposed research is to determine the relative fitness of individuals homozygous versus those heterozygous for MHC haplotypes in species experiencing severe reduction in population size (endangerment). Because of the impracticality of subjecting individual members of an endangered species to the rigors of a full immunogenetic analysis, a wild species with declining population size that is also available from game farms, the ring- necked pheasant, has been selected as the primary experimental animal. Present knowledge and expertise gained from previous work with the twelve known alloantigen systems of the chicken should permit identification of corresponding or similar systems, including the MHC, in the pheasant and, to the extent possible in truely endangered avian species of special interest such as various species of cranes. The alloantisera produced in blood- typed chicken stocks will serve as serological probes in the identification of alloantigen systems in the other avian species. As haplotypes are determined for the MHC, pedigreed family groups of pheasants showing genetic segregation will be used in collaborative physiological, developmental, and disease exposure studies to investigate the specific effects of particular haplotypes in homozygous and heterozygous individuals. Much progress has been made in understanding the cellular and structural basis for the immune functions of the MHC in the mouse and human. Considerable evidence indicates that the MHC of the chicken influences several fitness traits such as hatchability of fertile eggs, growth rate, and survival in juvenile and /or adult periods of the life cycle. As yet, however, there is no clear understanding of the adaptive function of the MHC in wild populations. The ring-necked pheasant is a species living in the wild that can readily be used to investigate the role of the MHC in survival. From the apparent universal presence of an MHC in all vertebrate species and the essential similarities in immune function across species so far investigated, it is highly likely that a knowledge of the essential function of the MHC in the adaptability of a wild species will be important in genetic planning for preservation of endangered species.