Antibodies are produced by the adaptive immune system and to antigens presented by a pathogen. The antibody-antigen complex is then detected by cytotoxic T-cells, which destroy the infected cell. The antibodies are created by B-lymphocytes, which can differentiate when exposed to a specific pathogen. Differentiated B-lymphocytes known as plasma cells are responsible for the mass production of certain antibodies.

Macrophages are derived from monocytes and serve as phagocytes in the innate immune response. Basophils are also part of the innate immune response and, along with mast cells, produce histamine to initiate the inflammatory response.

Acquired immunity is developed in the body following a previously encountered infection. The innate immunity is, by definition, always present in the body and is used to attack all general forms of infection.

The granulocyte cells are considered part of innate immunity and help mediate the immune response against foreign pathogens. These cells include basophils, neutrophils, eosinophils, mast cells, and macrophages (which are differentiated from monocytes).

The adaptive immune response involves the production of antibodies against specific target antigens. Plasma cells are an integral part of the adaptive response and secrete large volumes of antibodies in response to a secondary infection by a previously encountered pathogen. T-cells and B-cells are also part of the adaptive response.

There are many types of white blood cells with distinct functions in the body. Neutrophils and monocytes are phagocytes that engulf bacteria. B-lymphocytes produce one type of antibody. Basophils are the least common of the leukocytes, and release histamine during inflammation.

Before a B-lymphocyte can proliferate and differentiate, it must present its antigen to a helper T-cell. If the helper T-cell recognizes the antigen as foreign, it will activate the B-lymphocytes, and cause them to differentiate into plasma cells and memory B-cells.

The five types of leukocytes are: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Three of these (neutrophils, eosinophils, and basophils) contain granules, tiny sacs containing enzymes which can lyse microorganisms. The other two leukocytes (lymphocytes and monocytes) do not contain these granules.

T and B cells are both part of the adaptive immune response. This means that they are typically made to handle very specific pathogens that may be encountered in the body. Before they are released into circulation, both must undergo negative selection, which makes sure that they do not respond to natural peptides that they encounter in the body. Failure of this step to take place can result in autoimmune diseases.

Many of the modulations of the immune response are controlled by helper T cells. In order to change the type of antibody secreted by a B cell, helper T cells need to interact with them via a number of cytokines. The types of cytokines secreted by helper T cells will tell the B cells which antibodies to start secreting.

An antibody is very specific and will only attach to one antigen. Once it does, the antibody can signal the pathogen or infected cell to be destroyed by macrophages and other phagocytic cells in the body, such as cytotoxic T-cells. The antibodies themselves cannot destroy the pathogen.

T-cells serve important functions in the communication and stimulation of antibody production, but do not actually produce antibodies.

Antibodies are part of the adaptive immune response, which means that they are formed later in an infection. Because both recognition sites have the same structure, they are responsive to only one type of antigen. They are located on the outside of B cells, and can be released freely into the plasma by plasma cells.

Placental crossing is done mainly by IgG antibodies. These fast-acting antibodies provide temporary immunity for the fetus until it is able to have its own immune system produce sufficient antibody amounts.