INTRODUCTION AND DEFINITIONS
The term "humoral" refers to the non-cellular components of the blood, such as plasma and lymphatic fluid. The humoral immune response denotes immunologic responses that are mediated by antibodies. However, both B and T lymphocytes, as well as dendritic cells and other antigen presenting cells, are necessary for the formation of antigen-specific antibody.
Humoral immunity includes the primary and secondary immune responses to antigen. During the primary immune response, an antigen is encountered by the host for the first time. Virgin B cells need to be activated and proliferate before an effective immune response can be generated. This primary response may be too slow to protect against many pathogens, therefore polyspecific natural antibodies with low affinity and the innate immune system may be utilized to limit microbial replication at the onset of infection. By comparison, the secondary antibody response, which results from the activation of a memory B cell, is faster and more effective in halting the progress of infection due to increased antibody binding affinities.
Vaccination induces a primary immune response so that the patient produces the faster and more effective secondary response upon natural exposure to a pathogen, and is one of the most important contributions of immunology to disease prevention.
An overview of the humoral immune response will be provided here. Discussions of immunoglobulin structure, function, and genetics, as well as a review of B cell development are found separately. (See "Function and clinical applications of immunoglobulins" and "Immunoglobulin genetics" and "Normal B and T lymphocyte development".)
PASSIVE AND ACTIVE HUMORAL IMMUNITY
Passive humoral immunity is the acquisition of preformed antibodies from an external source, such as the administration of intramuscular or intravenous human immunoglobulin (Ig). (See "Medical management of immunodeficiency".)