Autoantigens are translocated into small apoptotic bodies during early stages of apoptosis

Abstract

A dysregulation of apoptosis or an ineffective clearance of apoptotic material is suspected to be involved in the pathogenesis of systemic lupus erythematodes. Subcellular fragments such as apoptotic bodies (ABs) have been recognized as modulators of intercellular communication and immune function. In this context, we have been interested whether nuclear and cytoplasmic antigens are relocated into ABs. In the present study, we characterized ABs isolated from apoptozing lymphoblasts. We found an accumulation of the linker-histone (histone 1) as well as the core-histones (histone 2A, histone 2B, histone 3, histone 4) in ABs. Further, they contained DNA, RNA and the ribonuclear protein La/SSB. Proteins such as cytochrome c, HSP 70, prohibitin, p53, nuclear matrix antigen or lamin B were excluded from ABs. The content of ABs differed from that observed in membrane microparticles isolated from viable cells. Formation of ABs occurred early during apoptosis. It was observed before DNAdegradation or phosphatidylserine exposure was detected. ABs were engulfed by monocyte-derived phagocytes. These findings suggest that immunogenic molecules are actively translocated into ABs followed by a rapid engulfment of the latter by environmental phagocytes. In autoimmune diseases, a defect in the clearance of ABs or AB formation may contribute to the development of autoimmunity.

Increased IgG on cell‐derived plasma microparticles in systemic lupus erythematosus is associated with autoantibodies and complement activation

“…It has been proposed that MPs carry autoimmunogenic material and ICs in SLE patients, and this is the first study to verify highly significantly increased concentrations of IgG-positive cell-derived MPs and a higher average IgG load on MPs from SLE patients compared with both disease controls and healthy controls (6,13,30,31). Exposure of autoantigens on circulating MPs in SLE patients has several implications.…”

The consequences of apoptosis in autoimmunity

“…The impact of apoptosis on immunity has been extensively investigated [2,13] and several reports suggest a correlation between apoptosis and autoimmunity through an impairment of apoptosis [14][15][16] or an ineffective removal of apoptotic cells [17][18][19][20]. Moreover, recent data have demonstrated that autoantigens are found within apoptotic bodies [21] and that apoptotic cells are critical in the presentation of antigens [22], activation of innate immunity and regulation of macrophage cytokine secretion [23]. Apoptotic bodies have been also described as B cell autoantigens [24].…”

Photopheresis with UV-A light and 8-methoxypsoralen leads to cell death and to release of blebs with anti-inflammatory phenotype in activated and non-activated lymphocytes

“…Depending on the stimulus, apoptotic cells also release microparticles and apoptotic blebs. As described by Schiller et al, we used the term blebs for sub-cellular particles that have separated from apoptozing cells [24]. Blebs can be modulators of regulators of immune responses, depending on the expression on their surface of PS, as well as of proteins derived from the cytosol, the endoplasmatic reticulum, and the nucleus [7].…”

“…During apoptosis cellular constituents are packed in membrane coated vesicles, in the so called apoptotic blebs. The latter are rapidly engulfed by environmental phagocytes [24]. Apoptotic cells and apoptotic cell-derived blebs acquire distinct surface determinants like PS for specific recognition by responder phagocytes leading to their antiinflammatory clearance [3].…”

“…Non-stimulated cells were cultured shortly in R10 medium and treated immediately. Blebs were identified and quantified with flow cytometry as previously described by Schiller et al [24].…”