Binding and internalization of human IgG by living cultured endothelial cells

Abstract

SUMMARYInteractions between circulating IgG and endothelial cells (EC) in humans have been described only in conditions associated with pathologic immunoglobulins and/or activated or damaged EC. In this study we provide evidence that normal human IgG includes one/some antibody species that bind to and are internalized by living EC in culture. This novel function of EC and natural autoantibodies is of potential importance for the understanding of physiologic interactions between vessels and the immune system and for the clarification of pathogenesis of vasculitis and mechanisms of action of pooled IgG used in the therapy of such conditions.

Spontaneous internalization of IVIg in activated B cells

“…Thus, although we could not rule out a possible contribution of FcRs or BCR to IVIg internalization in B cells, we conclude that there must be at least one other mechanism of internalization. Internalization of IVIg into living endothelial cells has been reported several years ago and was shown to depend on intact microtubules and to be independent of Fc␥Rs [27] suggesting that a similar pathway of internalization could be used in B cells. However, we showed that the non-selective process of fluid-phase pinocytosis could not account for IVIg internalization, since a control protein (HSA) used at the same dose was only minimally internalized.…”

Early Proinflammatory Activation of Renal Tubular Cells by Normal and Pathologic IgG

“…Given the general disregulation of autoantibody production in SLE, differences between the stimulatory action of normal IgG and IgG from SLE patients could be dependent on differences in composition between natural and SLE-associated autoantibodies reacting with tubular cells, in analogy with what has been observed with other specificities, e.g. anti-endothelial cells [21]. Indeed, when analyzing the pattern of IgG reactivity towards tubular cell extracts by Western blotting we found that SLE IgG used in our experiments differed from normal IgG in the recognition of tubular proteins.…”

Immunological evidence and regulatory potential for cell‐penetrating antibodies in intravenous immunoglobulin

“…2,5,7 IVIg has been previously reported to internalize in vitro, into certain cell types, namely endothelial, dendritic and B cells. [22][23][24] Individual normal IgG, tested in parallel with IVIg, showed similar penetrating profile, strongly suggesting that CPAbs do occur under physiological conditions. This may exclude the possibility that this effect was due to the wide range of reactivities present in IVIg or to spurious antibody contamination from undiagnosed diseases.…”

“…Although, it is documented that IVIg can be internalized by endothelial cells through ligand–FcR-mediated endocytosis, 22 it has been also reported that the spontaneous FcR-independent internalization of IVIg occurs in immune cells. 23, 24 Our results are in agreement with the latter, showing IVIg penetration in an energy-independent manner into a variety of cell lines several of which are not expressing Fc receptors.…”

“…Some indications only have been provided by the groups of A Borghetti and R Bazin reporting the internalization of intravenous immunoglobulin (IVIg), a therapeutic blood product of pooled normal human IgG, into certain cell types (endothelial, dendritic and B cells). [22][23][24] IVIg internalization was reported to occur via either an endocytosis-dependent mechanism or spontaneously via an unknown mechanism, followed by modulation of endothelial cell antiinflammatory response or by alteration of major histocompatibility complex class II antigen presentation, respectively. 24,25 In this study, we focused on unanswered issues concerning the contribution of specific antibody subpopulations in IVIg cell penetration and the subsequent effect(s) on cell function, as well as the biodistribution of IVIg post administration.…”