Helper T cell (T_H ) activation and differentiation is the central event that regulates both the components of immune response; CMI and AMI.

Activation of Helper T Cells

 Signal Generation

 Activation of TH cells requires generation of three specific signals (Fig. 1).

1. Antigen-specific signal: It involves binding of antigenic peptide present in the groove of MHC-II on APCs to TCR (T cell receptor) present on surface of T_H cells. CD4 molecules of T_H cells also interact with β2 domain of MHC-II

2. Costimulatory signal: It involves binding of CD28 molecule on T_H cells to B7 molecules on APCs

 3. Cytokine signal: APCs (macrophages) secrete interleukin-1 (IL-1) which acts on T_H cells.

Fig1. Activation of T_H cell by interacting with APC. Abbreviations: APC, antigen-presenting cells; MHC, major histocompatibility complex; TCR, T cell receptor.

Signal Transduction

 Following induction of signal, its transmission is essential for T_H cell activation. Signal transduction is initiated at CD4 molecule which interacts with CD3 complex, which in turn transmit the signal leading to activation of T_H cells.

Differentiation of Helper T Cells

Activated T_H cells secrete increased amount of IL-2 as well as IL-2 receptor (IL2R or CD25). IL-2 binds to its receptors on the same T_H cell and also on other T_H cells and induces the naive T_H cells to proliferate and differentiate. T_H cells get activated and become lymphoblast cells which subsequently differentiate into memory and effector TH cells.

 Effector T_H Cells

They are derived either from the naive T_H cells or pre-existing memory T_H cells following antigenic stimulus. They are short lived (few days to weeks). They further differentiate into either T_H 1 or T_H 2 subsets. This differentiation is very crucial as they secrete distinct cytokines that further mediate specific functions.

Cytokines secreted by T_H 1 cell stimulate cytotoxic T cells and induce cell mediated immune response; while cytokines secreted by T_H 2 cell stimulate B cells producing different classes of antibodies (humoral immune responses). IL12 secreted by macrophage plays an important role in the differentiation of TH cells. It promotes T_H 1 subset proliferation.

T_H 1 cells produce IL-2, interferon-γ (IFN- γ) and tumor necrosis factor-β (TNF-β); each has specific function (Table 1) T_H 2 cells secrete IL-4, IL-5, IL-6, IL-10 and IL-13. They activate the B cells to transform into plasma cells which in turn secrete antibodies (Table 1).

Table1. Role of cytokines secreted by T_H 1 and T_H 2 cells.

Memory T Cells

 They are derived from activated T_H cell. They have longer life span (months to years). They are in resting stage, but following subsequent antigenic stimulus, they become activated and differentiated into effector T_H cells. They express CD45RO isoform of common leukocyte antigen CD45, as compared to naive T cells which express CD45RA.

اخر الاخبار

اخبار العتبة العباسية المقدسة

وفد العتبة العباسية المقدسة يجري جولة في أروقة معرض بغداد الدولي للكتاب

شعبة التوجيه الديني النسوي تطلق برنامجًا قرآنيًّا لزائرات مرقد أبي الفضل العباس (عليه السلام)

جامعة الكفيل تطلق دورة تدريبية عن تقييم الأداء الجامعي لعدد من ملاكاتها

المجمع العلمي يقيم محفلًا قرآنيًا بذكرى ولادة الصادقين (صلوات الله عليهما)

المزيد

الآخبار الصحية

هل يتنبأ الذكاء الاصطناعي بأمراضنا قبل حدوثها؟

وداعا للنظارات.. قطرة عين واحدة قد تغير كل شيء ؟

دراسة تكشف تأثير "تيك توك" وتطبيقات الفيديو على سلوك الأطفال

"أسرار خفية" في الشاي الأخضر.. تغير قواعد الصحة والوزن

المزيد

الآخبار التكنلوجية

أول قطار يعمل بالهيدروجين في أميركا يدخل الخدمة رسميًا

أجهزة أبل القادمة.. "حصن منيع" في عصر الهجمات الرقمية !

روسيا: تطلق قمرين اصطناعيين بواسطة الصاروخ سويوز 2.1

ميزة ثورية.. أبل تدخل عالم قياس ضغط الدم

المزيد

مواضيع ذات صلة

Hypersensitivity Reactions

Humoral/Antibody-Mediated Immune Response

Cell-Mediated Immune Response

Type III (Immune Complex) Reactions

Influenza virus immunology

Type II Antibody-Dependent, Complement-Mediated Cytotoxic Reactions

Immunologic Manifestations of Rubella infection

Antigen presentation

Cytokines

Structure of MHC Molecule

MHC Genes and Their Products

Macrophage