A central question for immunology is: what does the immune system recognize and according to which principles does this kind of recognition work? Immunology has been dominated by the idea of recognizing molecular structures and triggering an appropriate immune response when facing non-self or danger. Recently, characterizations in terms of function have turned out to be more conserved and explanatory in microbiota research than taxonomic composition for understanding microbiota-host interactions. Starting from a conceptual analysis of the notions of structure and function, I raise the title question whether it is possible for the immune system to recognize microbial functions. I argue that this is indeed the case, making the claim that some function-associated molecular patterns are not indicative of the presence of certain taxa (‘‘who is there’’) but of biochemical activities and effects (‘‘what is going on’’). In addition, I discuss case studies which show that there are immunological sensors that can directly detect microbial activities, irrespective of their specific structural manifestation. At the same time, the discussed account puts the causal role notions of function on a more realist and objective basis.

免疫学的中心问题是：免疫系统会识别什么，并且根据哪种原理起作用？免疫学的主要思想是识别分子结构并在面对非自身或危险时触发适当的免疫反应。最近，事实证明，在功能方面的表征比在理解微生物群-宿主相互作用的分类学组成上更保守和更具解释性。从对结构和功能概念的概念分析开始，我提出了一个标题问题，即免疫系统是否可能识别微生物功能。我认为情况确实如此，声称某些与功能相关的分子模式并非指示某些分类单元的存在（“谁在那里”），而是生物化学活性和作用（“正在发生什么”）的指示。此外，我讨论了一些案例研究，这些案例表明，存在可以直接检测微生物活动的免疫传感器，而不论它们的具体结构如何。同时，所讨论的陈述将功能的因果角色概念放在更加现实和客观的基础上。