IntroductionThe function of the second receptor for the complement cleavage product C5a, C5aR2, is poorly understood and often neglected in the immunological context. Using mice with a global deficiency ofC5aR2, we have previously reported an important role of this receptor in the pathogenesis of the neutrophil-driven autoimmune diseaseepidermolysis bullosa acquisita(EBA). Based onin vitroanalyses, we hypothesized that the absence of C5aR2 specifically on neutrophils is the cause of the observed differences. Here, we report the generation of a new mouse line with a LysM-specific deficiency ofC5aR2.MethodsLysM-specific deletion ofC5aR2was achieved by crossingLysMcremice withtdTomato-C5ar2fl/flmice in which thetdTomato-C5ar2gene is flanked by loxP sites. Passive EBA was induced by subcutaneous injection of rabbit anti-mouse collagen type VII IgG. The effects of targeted deletion ofC5ar2on C5a-induced effector functions of neutrophils were examined inin vitroassays.ResultsWe confirm the successful deletion of C5aR2 at both the genetic and protein levels in neutrophils. The mice appeared healthy and the expression of C5aR1 in bone marrow and blood neutrophils was not negatively affected by LysM-specific deletion of C5aR2. Using the antibody transfer mouse model of EBA, we found that the absence ofC5aR2in LysM-positive cells resulted in an overall amelioration of disease progression, similar to what we had previously found in mice with global deficiency ofC5aR2. Neutrophils lacking C5aR2 showed decreased activation after C5a stimulation and increased expression of the inhibitory Fcγ receptor FcγRIIb.DiscussionOverall, with the data presented here, we confirm and extend our previous findings and show that C5aR2 in neutrophils regulates their activation and function in response to C5a by potentially affecting the expression of Fcγ receptors and CD11b. Thus, C5aR2 regulates the finely tuned interaction network between immune complexes, Fcγ receptors, CD11b, and C5aR1 that is important for neutrophil recruitment and sustained activation. This underscores the importance of C5aR2 in the pathogenesis of neutrophil-mediated autoimmune diseases.