Opsonization

Opsonization is the lateration of a pathogens or particles surface, either by the attachment of complement or antibodies specific for the antigen, so that it can be ingested (phagocytosed) by phagocytes, macrophages and neutrophils. Phagocytosis of the chicken RBCs occurred by macrophages present in the tissues and not by neutrophils that are present in the circulation. However the phagocytosing macrophages became activated by binding the antibody opsonized chicken RBCs and begin secreting inflammatory mediators and cytokines, such as IL-1, forming and maintaining a local inflammatory reaction with increased blood flow from dilated, nearby blood vessels which now also have increased permeability. This inflammation reactions allows leukocytes, including phagocytic neutrophils, to migrate out of the blood vessels (diapedesis) and into the infected cavity to aid in phagocytosis and ultimately in the clearance of the chicken RBCs. The macrophages which phagocytosed chicken RBCs, process these foreign particles and become antigen presenting cells, by presenting these particles on their surface MHC molecules (major histocompatibility complex). Moreover, any chicken RBCs that may have escaped phagocytosis and the ensuing inflammation response, would have been filtered through the afferent lymphatics near the mouse's diaphragm.

Lymphatics contain lymph, a viscous fluid containing water, ions, proteins, and also leukocytes. Where lymphatic vessels converge lymph nodes are found, which also contain lymphocytes. Lymphatics deliver antigen to lymph nodes, that have a high abundance of antigen-presenting cells, such as dendritic cells, where adaptive immune responses can be further initiated with circulating lymphocytes. In addition, lymph eventually drains into the left subclavian vein through the thoracic duct. Any chicken erythrocytes left in the lymph, would enter the bloodstream and pass through the spleen, where an adaptive immune response could occur and also activate the alternative complement pathway. C3b, the cleaved product of C3 generated by C3 convertase, can coat and opsonize the surface of the chicken RBCs, ligating the C3b receptor present on macrophage's and enhancing phagocytosis (1,4).

References:

1. Janeway, C.A., Travers P., Walport M., and Capra J.D. 1999. Immunobiology: The immune system in health and disease. Garland Publishing, 4th ed., New York, USA, pages 1-40, 2.5-2.22, 3.1-3.12

2. DeFranco, A.I. 1987. Molecular aspects of B-lymphocyte activation. Annu. Rev. Cell Biol. 3:143-178

3. MacLennan, I.C.M. 1994. Germinal centers. Annu. Rev. Immunol. 3:117-139

4. Ravetch, J.V. and Kinet, J. 1993. Fc receptors. Annu. Rev. Immunol. 9:457-492