Immune response to infections Factors influencing the extent and severity of infection •Pathogen factors –Dose –Virulence of organism –Route of entry •Host factors –Integrity of non-specific defences –Competence of the immune system –Genetic influences –Previous exposure to antigen –Existence of co-infection Immune response to viral infections –Non-speciphic immunity •Interferons ( a and b) •Natural killer cells (NK buňky) •Activation of the complement system (EBV) •Phagocytosis •Receptor-like molecules in various secretions –Speciphic immunity •Antibodies – neutralization of extracellular viruses •Tc lymphocytes – elimination of virus-infected cells Mechanisms of antiviral immunity protivirová imunita interferon2 The action of interferon (IFN) Natural killers (NK cells) •Originate in non-T non-B lymphocyte lineage. •Morphologically: large granulated lymphocytes (LGL). •Recognition of target cells in antigen non-speciphic. •Virus infected and tumor cells are killed. •Target cells are characterised namely by decreased HLA-I expression. •Cytotoxic mechanisms are similar to Tc cells: perforin and induction of apoptosis. Viral strategies to evade the immune response •Antigenic variations –antigenic drift - minor changes –antigenic shift - major changes •Long-term survival in a host –Viral persistence –Viral latency –Oncogenic transformation •Immunosuppressive effect of viruses Immunosuppressive effects of viruses •Suppression of T-cells : HIV, morbilli, CMV, •Inhibition of MHC antigens expression: CVM (binds b-2 microglobulin), Adenoviruses, RSV - decreases expression of HLA antigens •Production of inhibitory cytokies: EBV ( IL-10 - like factor) • Damage of a host caused by anti-viral immune response •Autoimmune diseases: hemolytic anemia after EBV infection, autoimmune hepatitis induced by hepatitis-B virus •Immune complex diseases: arthritis in hepatitis B, vasculitis •Tc - meadited diseases: rash in exanthematic viral diseases, myocarditis caused by coxackie virus Immune responses to bacterial infections •Non-specific immunity –Mechanical barriers –Phagocytosis –Complement system •Specific immunity –Antibodies - opsonisation, complement-activation, neutralisation of toxins, binding to receptors –T-lymphocytes - against intracellular parasites Bacterial evasions of immune defences •Antiphagocytic machanisms: toxins, capsular polysaccharides •Inhibition of the complement system: Str. pyogenes, E. coli, N. meningitidis •Antigenic variations: Borrelia recurrentis •Proteases lysing IgA - Neisseria, Haemophilus •Sequestration in avascular regions- Salmonella typhi in the gall bladder and urinary tract •Intracellular parasitism Bystander damage caused by the immune response to bacterial infection •Autoimmune diseases –Cross-reactivity of bacterial and corporal antigens - rheumatic fever –Type-II hypersensitivity - autoimmune hemolytic anemia caused by Mycoplasma infection –Heat shock proteins –Superantigens (streptococcal, staphylococcal) •Immunocomplex diseases •Type IV hypersensitivity- cavitatoin in pulmonary tuberculosis Suerantigeny Activation of TCR by antigen and superantigen Mechanisms of anti-fungal resistance •Normal bacterial flora •Phagocytic cells •T-lymphocytes -probably most important •Antibodies - usually present, but no protective effect