Neo-epitopes are required for immunogenicity of the La/SS-B nuclear antigen in the context of late apoptotic cells

Abstract

SummaryMechanisms responsible for the induction of anti-nuclear autoantibodies (ANA) following exposure of the immune system to an excess of apoptotic cells are incompletely understood. In this study, the immunogenicity of late apoptotic cells expressing heterologous or syngeneic forms of La/SS-B was investigated following subcutaneous administration to A/J mice, a nonautoimmune strain in which the La antigenic system is well understood. Immunization of A/J mice with late apoptotic thymocytes taken from mice transgenic (Tg) for the human La (hLa) nuclear antigen resulted in the production of IgG ANA specific for human and mouse forms of La in the absence of foreign adjuvants. Preparations of phenotypically healthy cells expressing heterologous hLa were also immunogenic. However, hLa Tg late apoptotic cells accelerated and enhanced the apparent heterologous healthy cell-induced anti-La humoral response, while non-Tg late apoptotic cells did not. Subcutaneous administration of late apoptotic cells was insufficient to break existing tolerance to the hLa antigen in hLa Tg mice or to the endogenous mouse La (mLa) antigen in A/J mice immunized with syngeneic thymocytes, indicating a requirement for the presence of heterologous epitopes for anti-La ANA production. Lymph node dendritic cells (DC) but not B cells isolated from non-Tg mice injected with hLa Tg late apoptotic cells presented immunodominant T helper cell epitopes of hLa. These studies support a model in which the generation of neo-T cell epitopes is required for loss of tolerance to nuclear proteins after exposure of the healthy immune system to an excess of cells in late stages of apoptosis.

Direct antigen presentation by DC shapes the functional CD8+ T‐cell repertoire against the nuclear self‐antigen La‐SSB

“…La protein or peptides induces T CD41 responses leading to polyclonal autoantibody production and intermolecular spreading of immunity [6,7,25]. In contrast, we show here that functional T CD81 specific to La protein in normal mice are not detectable, which suggests that self-tolerance in the T CD81 compartment is more tightly regulated than that in the T CD41 compartment.…”

“…Poor self-tolerance of some nuclear/cytoplasmic proteins and a propensity for them to become autoimmune targets could result from their sequestered localization [2], their low abundance or rapid turnover [3], and their exposure to antibodies during redistribution and concentration in apoptotic blebs [4]. Further, their association with RNA and the potential to stimulate TLR7 and 8 [5], coupled with defects in apoptosis and clearance of debris, renders some nuclear Ag as clinically relevant targets of autoimmunity [6,7]. Although much of the pathology in systemic autoimmunity is due to the deposition of complement-fixing immune complexes [8], CD81 T cells (T CD81 ) have increasingly been implicated in other autoimmune conditions [9,10].…”

“…The mean and standard deviation for each group (n 5 4) are shown; statistically significant differences (Mann-Whitney U test) are indicated. (C) T CD81 recruited to the peritoneum by rhLa-loaded A/J splenocytes, hLa.A/J-Tg splenocytes or EL4.hLa 51-58 were isolated and restimulated in vitro with graded amounts of hLa [51][52][53][54][55][56][57][58] La protein or peptides induces T CD41 responses leading to polyclonal autoantibody production and intermolecular spreading of immunity [6,7,25]. In contrast, we show here that functional T CD81 specific to La protein in normal mice are not detectable, which suggests that self-tolerance in the T CD81 compartment is more tightly regulated than that in the T CD41 compartment.…”

“…We have also demonstrated poor self-tolerance towards Tg hLa peptides in the MHC-II compartment of normal mice. Moreover, autoreactive CD41T helper cells alone are able to induce B cells to produce autoantibody [20] and apoptotic cell debris can be a source of La for autoimmunity [6]. In contrast, we know little about the process for shaping the repertoire of MHC-I restricted T CD81 to La autoantigen.…”

A B cell apotope of Ro 60 in systemic lupus erythematosus

“…Apotope-binding autoantibodies are more likely to represent the pathogenic species in conditions such as congenital heart block (CHB), in which maternal autoantibodies form IgG-apoptotic cell complexes in the vicinity of the fetal cardiac system and produce impaired clearance of apoptotic cardiocytes, promoting inflammation and subsequent scarring (9). Apoptotic cells are widely believed to serve as the source of intracellular immunogen for production of antinuclear antibodies, potentially via the generation of cryptic B and/or T cell epitopes (10). The definition of Ro and La apotopes may therefore provide new insights into the form in which these immunogens break immune tolerance and may also identify potentially pathogenic maternal autoantibodies in CHB.…”