Serum and organ‐associated anti‐hemoglobin humoral autoreactivity: Association with anti‐Sm responses and inflammation

Abstract

The release of hemoglobin (Hb) occurs in some infectious and autoimmune diseases characterized by inflammation. As levels of haptoglobin (Hp) fall, free Hb can cause pathology. Humoral autoreactivity to human Hb was demonstrated in the sera of systemic lupus erythematosus (SLE), leishmania and malaria patients. Serum anti-murine Hb antibody levels in lupus-prone mice also exhibited an age-dependent increase, with progressive organ sequestration; significant isotypic correlation was observed with antidsDNA antibodies. A suggestive link between anti-Hb and anti-Sm responses was observed: Human lupus sera expressing anti-Sm antibody reactivity preferentially contained heightened levels of anti-Hb autoantibodies, and immunization of lupus-prone mice with Sm led to enhanced anti-murine Hb reactivity. Human and murine anti-Hb monoclonal antibodies were generated, some of which were preferentially reactive toward disease-associated methemoglobin. Epitope-mapping studies revealed evidence of intramolecular cross-reactivity. One such autoantibody synergized with Hb to enhance the secretion of pro-inflammatory cytokines while eliciting the increased production of monocyte migratory signals from endothelial cells. Preferential usage of specific variable region gene segments was not observed, although somatic mutations were documented. These studies reveal that, while the etiology, specificity and sequences of anti-Hb autoreactive antibodies can vary, they occur quite frequently and can have inflammatory consequences.

Oxidized Hemoglobin Is Antigenic and Immunogenic in Lupus

“…Although the SLE patients constituted a distinct cross-sectional cohort, the incidence of anti-hHb reactivity was in general agreement with previous data from our lab (17); while anti-Hb antibody levels were also significantly elevated in sera of malaria patients, antibodies in sera from rheumatoid arthritis patients and vitiligo patients did not exhibit such reactivity (Figure 1A). IgG immunoglobulins were purified from the sera of eight SLE patients (demonstrating heightened anti-hHb reactivity) and eight control subjects by Protein G affinity chromatography; IgG purified from the sera of SLE patients demonstrated significantly higher reactivity toward hHb than did IgG purified from control sera (Figure 1B).…”

“…In this study, sera derived from a certain percentage of lupus patients exhibited anti-hHb humoral autoreactivity, in consonance with a previous report from our lab (17); IgG immunoglobulins purified from such sera also bound hHb. No obvious correlation was observed between autoimmune hemolytic anemia and the presence of anti-Hb antibodies.…”

“…Although T cell reactivity toward Hb (14) and anti-Hb autoantibodies (17) have been described in systemic autoimmunity, the immunobiology of Hb has not been investigated in detail. In this study, sera derived from a certain percentage of lupus patients exhibited anti-hHb humoral autoreactivity, in consonance with a previous report from our lab (17); IgG immunoglobulins purified from such sera also bound hHb.…”

“…Interestingly, in a specific instance, tumor-directed T cells were described to dominantly recognize Hb-derived peptides (15). Antigen microarray analysis of cord blood has revealed the existence of antibodies against Hb (16), and anti-Hb antibodies have been described in autoimmune human and murine sera (17). Humoral anti-Hb autoimmune responses remain poorly characterized, however, and potential mechanisms contributing to, as well as the downstream consequences of, a break of immunological tolerance to Hb are currently unknown.…”

Liver-inherent immune system: its role in blood-stage malaria

“…In accordance, it has been recently found that autoantibodies and sera from patients suffering from diverse autoimmune conditions, but not from malaria, inhibit the in vitro growth of P. falciparum in human RBCs (Bhatnagar et al, 2011; Brahimi et al, 2011). Especially that type of autoimmunity is apparently required for protection against blood-stage malaria (Daniel-Ribeiro, 2000), that is presumably directed against autoantigens and parasite-induced neo-autoantigens on the surface of Plasmodium -infected RBCs (Wunderlich et al, 1988b,c; Fontaine et al, 2012).…”