Phagocytosis and immunity

Abstract

The most important property of a great many nonpathogenic bacteria is a surface hydrophobicity that is higher than their mammalian hosts' phagocytes, so that they become automatically and readily phagocytized. Antibodies of the IgG and IgM classes cause the phagocytic removal of pathogenic hydrophilic bacteria by increasing their hydrophobicity and thus their proneness to phagocytosis by their hosts' phagocytes. This action is enhanced by the collective action of complement factors C1, 2, 4 and 3. The action of IgG in particular appears to be due to its hydrophobic Fc tail. Single IgG molecules, however, are too small to become phagocytized. Only antigen antibody complexes with at least three IgG molecules (two in the presence of complement) have a sufficiently low kinetic energy per surface area of attachment to become ingested by phagocytes. IgA does not increase the hydrophobicity of particles above the point where they can become readily phagocytized. This would tend to segregate IgA virus complexes extracellularly and thus may in part explain the anti viral role of IgA. Stimulation of macrophages, by MIF as well as by adjuvant like particles, results in an increase in their surface hydrophilicity, which gives rise to an enhanced capacity for phagocytosis. This increased surface hydrophilicity also causes the inhibition of the migration of macrophages in vitro, as well as their in vivo disappearance reaction. Not only specific antibodies can enhance the hydrophobicity of microorganisms and thus cause their disposal by phagocytes, but other, aspecific, serum factors may do so as well. At least one such aspecific serum factor (α2HS glycoprotein) has been identified as such and isolated. It is clear that many different specific and aspecific immunological effectors ultimately cause the enhancement of phagocytosis, either by decreasing the hydrophobicity of the surfaces of phagocytic cells or by increasing the hydrophobicity of the surfaces of the particles that are to be phagocytizied.