Endothelial cell (EC) activation determines CD32A and CD16‐dependent leukocyte recruitment in the presence of immune‐complexes and anti‐EC antibodies (AECA) found in SLE: cooperation with adhesion molecules and G‐protein coupled receptor signalling

Background Although AECA are commonly detected in serum of patients with SLE, their pathophysiological effects remain unclear. We have explored the hypothesis that they augment neutrophil (PMN)‐EC interactions. Methods We used a parallel plate flow‐chamber to study leukocyte adhesion to human microvascular EC. A mouse anti‐endoglin mAb (RMAC8) was used as a model anti‐EC antibody, with or without subsequent immune‐complex (IC) formation using rabbit anti‐mouse IgG. Human AECA were prepared from SLE patient serum. Results Under physiological flow, PMN failed to interact with resting EC, regardless of prior RMAC8, IC or AECA deposition. In contrast, RMAC8, IC or AECA significantly increased the number of PMN arresting on TNFα‐activated EC in a CD32‐dependent manner. Adenoviral expression of E‐selectin and ICAM‐1 molecules on unactivated EC resulted in increased PMN adhesion to IC coated EC in a CD16‐dependent manner, but was not sufficient for RMAC8 or AECA alone to stimulate leukocyte recruitment. Indeed, CD32‐dependent antibody mediated leukocyte adhesion to TNFα‐stimulated EC was inhibited by pertussis toxin, suggesting the additional requirement for an EC‐derived factor(s) acting via G‐protein coupled receptor(s). Conclusion These data show that CD32 and CD16‐ligation may each augment leukocyte recruitment at sites of local inflammation in SLE and other diseases characterised by the presence of AECA.