IntroductionA deep multi-omic analysis of post mortem human brains has identified a new co-expression protein network - Module 42 (M42), strongly corelated with Alzheimer's disease (AD) pathology. M42 comprises 32 transmembrane and extracellular matrix (ECM)-associated proteins, including the amyloid precursor protein (APP) and apolipoprotein E (apoE), and its members have been implicated in amyloid beta (Aβ) pathology. We systematically evaluated the Aβ-independent effects of M42 on immune function in vitro.MethodsRecombinant M42 proteins were expressed and purified. Their effects on phagocytosis, intracellular signaling, and cell viability were assessed in human induced pluripotent stem cell-derived macrophages.ResultsTreatment with Midkine (MDK) reduced phagocytosis, while treatment with the ectodomain of Transmembrane protein with EGF-like and two follistatin-like domains 2 (TMEFF2) had the opposite effect. Both proteins promoted intracellular Ca2+ signaling, and TMEFF2 also suppressed Syk kinase activity. No M42 proteins had an effect on viability.DiscussionOur results suggest an additional role for M42 in AD via regulating immune functions.HighlightsWe tested M42 proteins for their effects on immune functions in vitro. Five proteins altered phagocytosis, and seven altered Ca2+ signaling. MDK and TMEFF2 ectodomain had an effect on both phagocytosis and Ca2+ signaling.