Editing Immune system (section)

==== Gamma delta T cells ====
[[Gamma delta T cell]]s (γδ T cells) possess an alternative T-cell receptor (TCR) as opposed to CD4+ and CD8+ (αβ) T cells and share the characteristics of helper T cells, cytotoxic T cells and NK cells. The conditions that produce responses from γδ T cells are not fully understood. Like other 'unconventional' T cell subsets bearing invariant TCRs, such as [[CD1d receptor|CD1d]]-restricted [[natural killer T cell]]s, γδ T cells straddle the border between innate and adaptive immunity.<ref>{{cite journal | vauthors = Girardi M | title = Immunosurveillance and immunoregulation by gammadelta T cells | journal = The Journal of Investigative Dermatology | volume = 126 | issue = 1 | pages = 25–31 | date = Jan 2006 | pmid = 16417214 | doi = 10.1038/sj.jid.5700003 | doi-access = free }}</ref> On one hand, γδ T cells are a component of adaptive immunity as they [[V(D)J recombination|rearrange TCR genes]] to produce receptor diversity and can also develop a memory phenotype. On the other hand, the various subsets are also part of the innate immune system, as restricted TCR or NK receptors may be used as [[pattern recognition receptor]]s. For example, large numbers of human Vγ9/Vδ2 T cells respond within hours to [[non-peptidic antigen|common molecules]] produced by microbes, and highly restricted Vδ1+ T cells in [[epithelium|epithelia]] respond to stressed epithelial cells.<ref name="Holtmeier W, Kabelitz D 2005 151–83" />