<P> Gamma delta T cells (γδ T cells) possess an alternative T cell receptor (TCR) as opposed to CD4+ and CD8+ αβ T cells and share characteristics of helper T cells, cytotoxic T cells and natural killer cells . Like other' unconventional' T cell subsets bearing invariant TCRs, such as CD1d - restricted natural killer T cells, γδ T cells exhibit characteristics that place them at the border between innate and adaptive immunity . On one hand, γδ T cells may be considered a component of adaptive immunity in that they rearrange TCR genes via V (D) J recombination, which also produces junctional diversity, and develop a memory phenotype . On the other hand, however, the various subsets may also be considered part of the innate immune system where a restricted TCR or NK receptors may be used as a pattern recognition receptor . For example, according to this paradigm, large numbers of Vγ9 / Vδ2 T cells respond within hours to common molecules produced by microbes, and highly restricted intraepithelial Vδ1 T cells respond to stressed epithelial cells . </P> <P> B Cells are the major cells involved in the creation of antibodies that circulate in blood plasma and lymph, known as humoral immunity . Antibodies (also known as immunoglobulin, Ig), are large Y - shaped proteins used by the immune system to identify and neutralize foreign objects . In mammals, there are five types of antibody: IgA, IgD, IgE, IgG, and IgM, differing in biological properties; each has evolved to handle different kinds of antigens . Upon activation, B cells produce antibodies, each of which recognizing a unique antigen, and neutralizing specific pathogens . </P> <P> Antigen and antibody binding would cause five different protective mechanism: </P> <Ul> <Li> Agglutination: Reduces number of infectious units to be dealt with </Li> <Li> Activation of complement: Cause inflammation and cell lysis </Li> <Li> Opsonization: Coating antigen with antibody enhances phagocytosis </Li> <Li> Antibody - dependent cell - mediate cytotoxicity: Antibodies attached to target cell cause destruction by macrophages, eosinophils, and NK cells </Li> <Li> Neutralization: Blocks adhesion of bacteria and viruses to mucosa </Li> </Ul>

When does the immune system generate antigen receptors