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Bacteria and viruses use an array of evasion mechanisms to escape from the host immune system. Due to antigenic variation, pathogenic micro-organisms can escape the immune system. Micro-organisms can occur in different types, such as the 97 serotypes of Streptococcus pneumoniae. Influenza viruses change their antigenic make-up, in particular, the hemagglutinin molecule by antigenic drift and antigenic shift. Trypanosomes and malaria parasites use DNA programmed expression of highly variable surface antigens. Micro-organisms can also produce proteins that degrade (IgA protease) or inactivate antibody molecules (protein A and protein G). Some bacteria and viruses produce proteins that inhibit complement activation. Virus can become invisible for recognition by T-lymphocytes by interference with antigen presentation. Antiviral immunity can be suppressed by viral homologues of cytokines and cytokine receptors and other proteins. Despite the extensive immune evasion strategies used by viruses, bacteria and other micro-organisms, the immune system in most cases is ultimately able to control an infection.