These cells recognise peptides presented on HLA class II molecules (HLA-DR, HLA-DP and HLA-DQ) and have mainly immunoregulatory functions. They produce cytokines and provide co-stimulatory signals that support the activation of CD8 ⁺ T lymphocytes and assist the production of mature antibody by B cells. In addition, their close interaction with phagocytes determines cytokine production by both cell types. CD4 lymphocytes can be further subdivided into subsets on the basis of the cytokines they produce:

 -  Th1 (T-helper) cells typically produce IL-2, IFN-γ and TNF-α, and support the development of delayed-type hypersensitivity responses.

- Th2 cells typically produce IL-4, IL-5, IL-10 and IL-13, and promote allergic responses.

- T-regulatory cells (T-regs) are a further subset of specialised CD4 ⁺ lymphocytes that are important in actively suppressing activation of other cells and preventing autoimmune disease. They produce cytokines such as TGF-β and IL-10.

- Th17 cells are pro-inflammatory cells defined  by their production of IL-17. They are related to regulatory T cells. Th17 cells have a key role in defense against extracellular bacteria and fungi. They also have a role in the development of autoimmune disease.

 T-cell activation is regulated by a balance between co-stimulatory molecules , the second signal required for activation, and inhibitory molecules that down-regulate T-cell activity. One such inhibitory molecule, CTLA4, has been harnessed therapeutically in the form of abatacept, which is a fusion protein comprised of the Fc fragment of immunoglobulin linked to CTLA4. This is used to inhibit T-cell activation in rheumatoid arthritis and solid organ transplantation.

مواضيع ذات صلة

Tumour immunology

دور الغدة الدرقية

عرض الانتجينات الخارقة super antigens

الخلايا العارضة للمستضدات

Mediators of Inflammation and the Interferons

Natural Killer Cells

Properties of MHC Genes and Proteins

Structure of Class I MHC Molecules

معقدات التوافق النسيجي الكبرى ودورها في الاستجابة المناعية

اعادة تدوير الخلايا اللمفاوية Lymphocyte Recirculation

فرضية الانتقاء الوراثي او اختيار النسيلة Clonal selection hypothesis

الخلايا التائية المساعدة Helper T cells