Adaptive immunity is defined by the invocation of a specific
cellular immune response, in contrast to innate immunity that is
distinguished by a non-specific immunity. Adaptive responses
involve lymphocytes and are characterized two ways, humoral and
cell-mediated immunity. B cells mediate a humoral response, the
creation of antibodies to bind specifically to foreign antigens
including bacteria, and microbial toxins. Cell-mediated immunity
is a more complex system involving the production of cytotoxic
T-lymphocytes, activated macrophages, activated NK cells, and
cytokine release in response to an antigen and is mediated by
T-lymphocytes. T cells recognize a pathogen only after antigens
(small fragments of the pathogen) have been processed and
presented typically in combination with a “self” receptor called
a major histocompatibility complex (MHC) molecule. Cell-mediated
immunity is important in combating intracellular organisms,
performing tumor surveillance, mediating transplant rejection,
and fighting funga