Data from: Genes of the major histocompatibility complex highlight interactions of the innate and adaptive immune system

Background: A well-functioning immune defence is crucial for fitness, but our knowledge about the immune system and its complex interactions is still limited. Major histocompatibility complex (MHC) molecules are involved in T-cell mediated adaptive immune responses, but MHC is also highly upregulated during the initial innate immune response. The aim of our study was therefore to determine to what extent the highly polymorphic MHC is involved in interactions of the innate and adaptive immune defence and if specific functional MHC alleles (FA) or heterozygosity at the MHC are more important. Methods: To do this we used captive house sparrows (Passer domesticus) to survey MHC diversity and immune function controlling for several environmental factors. MHC class I alleles were identified using parallel amplicon sequencing and to mirror immune function, several immunological tests that correspond to the innate and adaptive immunity were conducted. Results: Our results reveal that MHC was linked to all immune tests, highlighting its importance for the immune defence. While all innate responses were associated with one single FA, adaptive responses (cell-mediated and humoral) were associated with several different alleles. Discussion: We found that repeated injections of an antibody in nestlings and adults were linked to different FA and hence might affect different areas of the immune system. Also, individuals with a higher number of different FA produced a smaller secondary response, indicating a disadvantage of having numerous MHC alleles. These results demonstrate the complexity of the immune system in relation to the MHC and lay the foundation for other studies to further investigate this topic.

研究背景：功能健全的免疫防御对于生物体适合度至关重要，但目前学界对免疫系统及其复杂相互作用的认知仍存在局限。主要组织相容性复合体（Major Histocompatibility Complex, MHC）分子参与T细胞介导的适应性免疫应答，而MHC在初始固有免疫应答过程中也会被高度上调。因此本研究旨在明确高度多态性的MHC在固有与适应性免疫防御相互作用中的参与程度，并探究特异性功能性MHC等位基因（Functional Alleles, FA）与MHC位点杂合性何者更为关键。
研究方法：为此，本研究以圈养家雀（Passer domesticus）为研究对象，在控制多种环境因素的前提下，对其MHC多样性与免疫功能进行调查。本研究采用平行扩增子测序技术鉴定MHC I类等位基因，并通过多项对应固有免疫与适应性免疫的免疫学实验来表征免疫功能。
研究结果：本研究结果显示，MHC与所有免疫学实验指标均存在关联，凸显了其在免疫防御中的重要性。所有固有免疫应答均与单一功能性等位基因相关，而适应性免疫应答（包括细胞介导免疫与体液免疫）则与多种不同的等位基因相关联。
讨论与分析：本研究发现，对雏鸟与成体反复注射抗体的操作与不同的功能性等位基因存在关联，因此该操作可能会影响免疫系统的不同功能区域。此外，携带更多不同功能性等位基因的个体其二次免疫应答强度更低，这表明拥有大量MHC等位基因可能存在劣势。本研究结果阐明了免疫系统与MHC之间的复杂关联，为后续相关领域的深入研究奠定了基础。