Lachnospiraceae and the Host Immune System: Mechanisms, Disease Associations and Precision-Oriented Intervention

The family Lachnospiraceae is among the most abundant obligately anaerobic taxa in the healthy human gut. Its core function—fermentation of dietary fibre to produce short-chain fatty acids (SCFAs), chiefly butyrate—makes it a key node linking diet, the microbiota and host immunity. Altered Lachnospiraceae abundance is associated with inflammatory bowel disease, colorectal cancer and autoimmune conditions, but the underlying molecular layers, causal structure and intra-family heterogeneity have yet to be integrated. This review addresses a single question: how do Lachnospiraceae shape and constrain host immunity? It first summarises the family’s taxonomy, metabolism and ecology, and then examines the relevant mechanisms along four partly overlapping axes of immune crosstalk: the mucosal barrier and epithelial innate immunity, metabolite-mediated immune signalling, immune sensing of bacterial structural components and the shaping of adaptive immunity, together with a fifth, prospective and still exploratory layer of immune tolerance and trained immunity, which is presented as an open question rather than as an established mechanism. Four features distinguish this review from earlier overviews of the family: an explicit evidence hierarchy applied claim by claim; strict separation of findings obtained for Lachnospiraceae from those obtained for related taxa; explicit grading of intervention studies according to whether the family was manipulated, depleted or merely measured; and restriction of the trained-immunity layer to an open question. Associations with immune-related diseases are then assessed by disease category, followed by culturomics, genetic tools, live biotherapeutic products (LBPs) and polysaccharide-based, precision-oriented interventions. The central conclusion is that the immunological effects of Lachnospiraceae are strongly strain-specific and disease-context-dependent; family-level associations therefore cannot be extrapolated directly to strain-level causal effects.