Mast cell functions in allergic responses by release histamine and other chemicals that promote inflammation. Macrophages are part of the innate immune system and function to engulf and remove debris. Neutrophils are also part of the innate immune system and have macrophagic properties, especially when fighting bacterial infection. Natural killer cells bind to and destroy pathogens without the use of antigens.

Neutrophils are responsible for destroying bacteria, eosinophils respond to parasitic worms and allergens, lymphocytes destroy cancerous or infected cells, and monocytes phagocytize pathogens and debris.

Selectins are most involved in the process of leukocyte rolling—or diapedesis—while ICAMs and integrins are involved in leukocyte firm and CD31 is involved in leukocyte transmigration.

During endothelial cell retraction, gaps form between the cells as their cytoskeletons are rearranged to decrease the cell's area. This is a result of histamine, which causes increased vascular permeability; endothelial cell retraction allows fluids to pass between the cells, contributing to the inflammatory effects of histamine.

An ELISA test would best look at antigens present in serum by using secondary antibodies to bind to antigen-antibody complex and change color, showing if an antigen is present. DNA microarray would just show genes activated. Precipitation and agglutination reactions are not as sensitive as ELISA.