Phagocytosis and oxycytosis: two arms of human innate immunity.

Human innate immunity operates in two compartments: extravascular (the tissues) and intravascular (the bloodstream). Physical conditions (fluid dynamics) in the compartments are different and, as a result, bactericidal mechanisms and involved cells are different as well. In relatively static media (the tissues, lymph nodes), bacteria are killed by phagocytes; in dynamic media (the bloodstream), bacteria are killed by erythrocytes. In the tissues and lymph nodes, resident macrophages and transmigrated from blood leukocytes (neutrophils and monocytes) recognize, engulf, kill, and digest bacteria; the clearance of the bloodstream from bacteria is performed by oxycytosis: erythrocytes catch bacteria by electric charge attraction and kill them by the oxygen released from oxyhemoglobin. Killed by erythrocytes, bacteria are decomposed and digested in the liver and the spleen. Phagocytosis by leukocytes in the tissues and oxycytosis by erythrocytes in the bloodstream are the main bactericidal mechanisms of human innate immunity.

Serum and organ-associated anti-hemoglobin humoral autoreactivity: association with anti-Sm responses and inflammation.

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 anti-dsDNA 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 intra-molecular 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 haemoglobin as antigenic target of cell-mediated immune reactions in patients with carotid atherosclerosis.

Atherosclerosis is a chronic inflammatory disease in which immune responses play a crucial role. Evidence exist demonstrating the involvement of autoimmune mechanisms in atherogenesis. Our aim in this study was to evaluate the possible role of human oxidized haemoglobin (Hb) as antigenic target of cell-mediated immune reactions in carotid atherosclerosis. PBMC from 44 patients and 24 healthy subjects, and T lymphocytes isolated from 9 carotid atherosclerotic plaques were tested by cell proliferation assay and by ELISA for cytokine production in response to oxidized Hb. This molecule induced a proliferative response in 21 of 44 (48%) patients' PBMC samples, in 12 of 24 (50%) healthy subjects' PBMC samples and in 2 of 9 (22%) infiltrating T lymphocyte samples. Cells from patients proliferating in response to oxidized Hb showed high levels of the pro-inflammatory cytokines interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha. Our findings implicate oxidized Hb as a possible antigenic target of cell-mediated immune responses contributing to inflammation in the pathogenesis of carotid atherosclerosis.