Macrophage subpopulations in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a heterogeneous group of autoimmune disorders defined by a consensus of clinical and laboratory criteria. Much of the pathophysiology and therapy of SLE has focused on autoimmune B and T cells of the adaptive immune system. Recently, the role of macrophages, part of the innate immune system, in SLE pathogenesis has gained attention. The field of immunology in general has recently changed in the way that it approaches macrophages. Rather than viewing them as a single, concrete whole, it has become clear that different subpopulations of macrophages contribute to various immune and non-immune processes. Such a nomenclature may provide an ideal framework from which to study macrophage pathogenesis in SLE. Studies suggest that M1 subtype macrophages play an important inflammatory role in SLE pathogenesis. Further, apparently reduced populations of M2a and M2c subtype macrophages may contribute to the lack of anti-inflammatory activity apparent in the disease. M2b subtype macrophages may actually have a role in causing disease directly. Regulatory macrophages have yet to be explored thoroughly in SLE, though the presence of a few of their markers may mean that they are active in suppressing SLE-related inflammation.