Evasion of Phagocytosis

By inhibition of chemotaxis and Complement

Strep. pyrogenes

Streptococcal chemokine protease - degrades the neutrophil chemokine (IL-8)

C5a peptidase

By Capsules

Slime layer, glycocalyx --> slippery surface making phagocytic cells to engulf

By anti-opsonins

M-protein binds serum factor H, destroying C3 convertase and preventing C3b opsonization -> prevent phagocytosis. e.g. group A Strep (S. pyrogenes)

Protein A binds the Fc portion of IgG in Staph. aureus

Pili

The pili of Neisseria gonorrheae are anti-phagocytic, although this is not true of all pili

Evasion of Acquired Immunity

By Antigenic variation

• N. gonorrheae: pili and outer membrane proteins
• Enterobacteriaceae: capsular and flagellar antigens
• Many viruses (esp. HIV): high mutation rates cause antigenic drift (--> epidemics)
• Segmented viruses (esp. influenza virus): reassort their genomes causing antigenic shift (--> pandemics)
• African trypanosomes: variant specific glycoprotein