Interaction of phagocytes with other blood cells and with pathogenic and nonpathogenic microbes.

Owing to the high surface tension of blood cells and to the equally high surface tension of their liquid habitat, the Hamaker coefficients A131 of blood cells (subscript 1) in blood (subscript 3), are unusually small; they are of the order of 0.25 to 2.5 X 10(-16) ergs. The very small van der Waals attractions such low Hamaker coefficients give rise to, coupled to the medium low but still sizable negative xi-potentials (-11 to -18 mV) of the cells, which cause an appreciable mutual electrostatic repulsion between blood cells, have been used to elaborate potential energy vs. distance diagrams, which closely reflect the unusual stability of blood cells in blood. When bacteria find their way into the bloodstream, they initially form an almost equally stable suspension. However, relatively hydrophobic nonpathogenic bacteria quickly aspecifically adsorb immunoglobulin G (IgG) molecules from blood serum, whilst hydrophilic pathogenic bacteria sooner or later also become coated with specific antibody molecules of the IgG-class. Through receptor sites on the surface of phagocytic blood cells, which can specifically bind to the Fc tails of IgG molecules, bacteria are first bound and then removed from the blood circulation and surrounding tissues. These Fc-receptor bonds presumably also are of a combined van der Waals and electrostatic nature. Thus in the normal course of events and by purely physicochemical mechanisms, phagocytic leukocytes will neither interfere with other leukocytes nor with any other blood cells, whilst they specifically interact with microorganisms and other unwanted foreign particles via IgG-IgG-receptor interactions. Also discussed, in the light of the principles elaborated above, are: some of the antiphagocytic mechanisms developed by certain pathogenic bacteria; the phagocytic disposal of aged, weak, or abnormal blood cells; and the role played by immunoglobulins other than IgG, and by complement, in the removal of bacteria and viruses.