Until recently, the function of B cell-derived antibodies in central nervous system (CNS) demyelinating disorders has mainly consisted in amplifying ongoing demyelination by complement fixation. With the discovery of antibodies against the water channel aquaporin-4 in the serum of neuromyelitis optica patients, evidence condensed that autoreactive antibodies may also elicit CNS inflammation. However, for another subgroup of patients with CNS demyelinating disorder, which show antibodies against myelin oligodendrocyte glycoprotein (MOG) in the blood, the precise role of these antibodies remains unknown.
We hypothesize that in anti-MOG antibody positive patients, MOG-reactive antibodies in the periphery are capable of opsonizing endogenous MOG protein, subsequently triggering CNS inflammation and demyelination. To prove this assumption, we intend to investigate the effect of serum from these patients on the internalization of soluble and membrane-bound MOG protein by generated human antigen-presenting cells.
For the generation of dendritic cells and macrophages, CD14+ myeloid cells were isolated from human peripheral blood mononuclear cells of healthy donors and cultured in the presence of distinct cytokines. Expression of Fcγ receptors as well as antigen uptake by the generated antigen-presenting cells were analyzed by flow cytometry.
Flow cytometry analysis of the generated cells revealed that macrophages highly expressed Fcγ receptors I, II and III. By contrast, dendritic cells only highly expressed Fcγ receptor II. Both dendritic cells and macrophages internalized fluorescently labeled MOG and ovalbumin protein, and the addition of a phagocytosis inhibitor diminished protein uptake. Furthermore, the phagocytosis activity of the generated cells was increased in the presence of rabbit anti-ovalbumin antibodies, indicating that soluble protein can be functionally opsonized by these antibodies.
Generated antigen-presenting cells were capable of internalizing soluble protein and rabbit anti-ovalbumin antibodies mediated opsonization of ovalbumin protein, resulting in an enhanced antigen uptake. In ongoing experiments, we investigate the effect of whole immunoglobulin G from anti-MOG antibody positive patients on the internalization of soluble and membrane-bound MOG protein by human antigen-presenting cells.