Stimulation of Eryptosis by Anti-A IgG Antibodies

Abstract

Anti-A IgG antibodies have previously been shown to stimulate Ca²⁺ entry into red blood cells. Increased cytosolic free Ca²⁺ concentration is known to trigger eryptosis, i.e. suicidal erythrocyte death, characterized by exposure of phosphatidylserine at the erythrocyte surface. As macrophages are equipped with phosphatidylserine receptors, they bind, engulf and degrade phosphatidylserine exposing cells. The present experiments have been performed to explore whether anti-A IgGs trigger phosphatidylserine exposure of erythrocytes. Phosphatidylserine exposure was estimated from annexin-V binding as determined in FACS analysis. Exposure to anti-A IgGs (0.5 µg/ml) indeed significantly increased annexin-V binding in erythrocytes with blood group A, but not in erythrocytes with blood group 0. According to Fluo3 fluorescence, anti-A IgGs increased cytosolic Ca²⁺ concentration. Whole cell patch clamp recordings revealed the activation of a Ca²⁺-permeable cation channel following treatment with anti-A-IgGs. Annexin-V binding following anti-A IgG exposure was blunted by Ca²⁺ removal while anti-A IgG-stimulated cation channel activity was not dependent on extracellular Ca²⁺. Osmotic shock (exposure of erythrocytes to 850 mOsm) increased annexin binding, an effect further enhanced by exposure to anti-A IgGs. In conclusion, anti-A IgGs activate erythrocyte cation channels leading to Ca²⁺ entry and subsequent erythrocyte cell membrane scrambling. The effect most likely contributes to the elimination of erythrocytes following an immune reaction against the A antigen.

IgA-mediated human autoimmune hemolytic anemia as a result of hemagglutination in the spleen, but independent of complement activation and FcαRI

“…Furthermore, our results exclude a role for ADCC and antibody-induced eryptosis as a possible cause of the RBC destruction in our patient, although such mechanisms have recently been proposed for the development of anemia associated with different types of anti-RBC antibodies. 22,29 The lack of in vitro erythrophagocytosis is consistent with the histologic finding of few signs of erythrophagocytosis in the spleen. Instead, we observed a RBC sequestration due to the marked accumulation of agglutinated RBCs in the spleen.…”

“…22 After incubation for 24 hours, e-IgA autoantibodies induced no significant increase in PS exposure and cytosolic Ca 2ϩ concentrations over those obtained for nontreated RBCs (supplemental Figure 3). Thus, e-IgA autoantibodies were not considered to cause cytotoxic effects on RBCs through the activation of eryptosis.…”

Erythrocyte programmed cell death

“…Suicidal erythrocyte death could be triggered by ligation of specific surface antigens, such as glycophorin-C (41), the thrombospondin-1 receptor CD47 (42) and the death receptor CD95/Fas (43). Further stimulators of eryptosis include ceramide (acylsphingosine) (44), prostaglandin E 2 (45), platelet activating factor (46), anti A IgG antibodies (47), hemolysin from Vibrio parahaemolyticus (48), listeriolysin (49), paclitaxel (50), amantadine (51), azathioprine (52), retinoic acid (53), chlorpromazine (54), cyclosporine (55), methylglyoxal (56), amyloid peptides (57), anandamide (58), Bay-Y5884 (59), curcumin (60), valinomycin (61), aluminium (62), mercury (63), lead (64), gold (65), vanadium (66) and copper (67).…”

Monoclonal auto-antibodies and sera of autoimmune patients react with Plasmodium falciparum and inhibit its in vitro growth

“…Second, Mo-autoAb may induce parasite or erythrocyte death. Eryptosis is a suicidal erythrocyte death process similar to apoptosis, which can be triggered by various stimuli including anti-blood group A IgG antibodies (Attanasio et al 2007) and it has recently been shown that P. falciparum erythrocytes die by an autophagic-like cell death under antimalarial pressure (�otino et al 2008). In that way, Mo-autoAb could react with components of the pRBC or parasite membrane and cause metabolic disturbances, for example an increase in the cytosolic Ca +2 concentration, triggering eryptosis or parasite cell death and inhibiting parasite growth.…”