Introduction to the Immune Response

In this chapter we provide an overview of the immune system and its vital role maintaining human health. Immune responses require the coordinated action of leukocytes that travel the body to eliminate threats posed by trauma, infection, toxins, and cancer. Leukocytes communicate via direct contact and via production and receipt of soluble proteins and intercellular messenger proteins called cytokines. Complete clearance of unwanted entities may involve both innate and adaptive leukocyte responses, which influence each other. Some innate mechanisms require no induction and are completely non-specific, whereas others are inducible and involve broad receptor-mediated recognition of a limited number of pathogen-associated or damage-associated molecular patterns (PAMPs/DAMPs). Adaptive responses involve the selective activation of lymphocytes via engagement of their antigen receptors by a specific foreign antigen. The three major subsets of lymphocytes are T helper cells (Th), cytotoxic T cells (Tc) and B cells, which use distinct mechanisms to recognize antigen and carry out different effector functions. Immune system malfunction can contribute to many clinical illnesses including autoimmune disorders, allergies, immunodeficiencies, chronic inflammation and cancer.