Review paper
Effects of staphylococcal hemolysins on the immune system of vertebrates

Staphylococcus aureus is pathogenic to animals and humans and produce many virulence factors such as hemolysins which include alpha-, beta-, gamma- and delta-hemolysin. These agents play a very important role in staphylococcal pathogenesis. Hemolysins are cytolytic to a variety of host cells. Toxicity to immune cells makes them a good means for staphylococci to avoid phagocytosis and other forms of immune response. Alpha-hemolysin is a protein toxin released to host environment as a monomer. Oligomerization of the monomers to a heptamer on the surface of the target cell results in a transmembrane pore formation usually leading to metabolic instability and cell lysis. The toxin targets many types of immune cells monocytes, neutrophils and lymphocytes usually causing their death at high concentrations, however at lower concentrations some stimulatory effects on various immune functions were observed. Beta-hemolysin known as an inflammatory inducer is an enzyme with a specific, other than for most of staphylococcal toxins mode of action and its effects depend on sphingomyelinase content in a target cell. Gamma-hemolysins are very unique bicomponent pore-forming toxins consisting of S and F class proteins, released as monomers and forming heterooligomers leading to a cation-selective channel formation. Human monocytes, macrophages and neutrophils are the main cell types susceptible to these bacterial agents. Delta-hemolysin, a heat-stabile, small protein produced by most Staphylococcus aureus strains acts as a cytolysin but also turned out to be a potent polyclonal activator of lymphocytes. Currently, staphylococcal hemolysins are being introduced to many fields of biotechnology.