The innate immune system is the host’s first line of defense against pathogens. Toll-like receptors (TLRs) are pattern recognition receptors that mediate recognition of pathogen-associated molecular patterns. TLRs also activate signaling transduction pathways involved in host defense, inflammation, development, and the production of inflammatory cytokines. Innate immunodeficiencies associated with defective TLR signaling include mutations in NEMO, IKBA, MyD88, and IRAK4. Other innate immune defects have been associated with susceptibility to herpes simplex encephalitis, viral infections, and mycobacterial disease, as well as chronic mucocutaneous candidiasis and epidermodysplasia verruciformis. Phagocytes and natural killer cells are essential members of the innate immune system and defects in number and/or function of these cells can lead to recurrent infections. Complement is another important part of the innate immune system. Complement deficiencies can lead to increased susceptibility to infections, autoimmunity, or impaired immune complex clearance. The innate immune system must work to quickly recognize and eliminate pathogens as well as coordinate an immune response and engage the adaptive immune system. Defects of the innate immune system can lead to failure to quickly identify pathogens and activate the immune response, resulting in susceptibility to severe or recurrent infections.

先天免疫系统是宿主抵御病原体的第一道防线。Toll 样受体 (TLR) 是介导病原体相关分子模式识别的模式识别受体。TLR 还激活参与宿主防御、炎症、发育和炎性细胞因子产生的信号转导通路。与 TLR 信号缺陷相关的先天性免疫缺陷包括NEMO、IKBA、MyD88和IRAK4突变. 其他先天免疫缺陷与对单纯疱疹病毒性脑炎、病毒感染和分枝杆菌病以及慢性粘膜皮肤念珠菌病和疣状表皮发育不良的易感性有关。吞噬细胞和自然杀伤细胞是先天免疫系统的重要成员，这些细胞的数量和/或功能缺陷会导致反复感染。补体是先天免疫系统的另一个重要组成部分。补体缺陷可导致对感染、自身免疫或免疫复合物清除受损的易感性增加。先天免疫系统必须能够快速识别和消除病原体，并协调免疫反应并参与适应性免疫系统。