Opsonization is a process, in which opsonins adsorb to the surface of bacteria or other particles and facilitate their adherence to the phagocyte cytoplasmic membrane through opsonin receptors. Specific binding between the particle and phagocyte which occurs during immune phagocytosis is mediated by immunoadherent receptors. It means that function of opsonins in the first case is realized by antibodies and in the second case by iC3b. To the phagocytosis itself chemotaxis of phagocytes precede into the site where phagocytosable material occurs. This is regulated by chemotactic factors generated by infectious agents themselves, as well as those release as a result of their initial contact with phagocytes and other components of the immune system.
Phagocytosis is a complex process composed of several morphological and biochemical steps.
It is responsible for the production of superoxide and other oxygen radicals, and also for the secretion of a variety of enzymes and biologically active substances controlling inflammatory and cytotoxic reactions. This step is of the first importance because during it two categories of cytotoxic substances, present in the preformed state in azurophil and specific granules and synthesized de novo during the respiratory burst, arrive at the same cell compartment. This degranulation normally prevents release of the toxic components into the extracellular milieu. However, some target may be too large to be fully phagocytosed or they avoid engulfment, resulting in frustrated phagocytosis in which no phagosome is formed. These may be killed extracellularly.