In general, the more active the host response, the greater the cellular injury. Viral infections in naive individuals induce a host response that is initially rapid and non-specific and then delayed and specific. The non-specific response occurs within hours of the development of viremia and contains viral loads, while the specific T and B cell responses occur after days and lead to eradication of infection and provide immunity from further infection. Cytokines are important in both specific and non-specific responses, being secreted in response to endogenous or exogenous antigen or bacterial products. Cytokines may kill virally-infected cells.
Complement activation is one of the earliest responses to infection.
Immune complexes activate the classical pathway of complement leading to recruitment of inflammatory cells including phagocytes which can destroy pathogens. But they can also lead to immune complex damage, as in cryoglobulinemia with vasculitis and glomerulonephritis. The type and strength of the immune response determines whether the individual will clear infection, become immune to further infection, or develop chronic disease. The individual's own genetic background will determine the type and strength of the immune response. The array of cytokines produced may determine whether an individual will respond favorably or unfavorably to an infection.