T Cell Development and Activation

Flashcards for reviewing T cell development, activation, and related terminology.

Adaptive Immunity

An immune response that becomes more powerful following repeated encounters with the same antigen

Why do we need T cells?

T cells aid the clearance of phagocytosed and intracellular microbes in macrophages and infected cells, respectively. They also help B cells produce different Ig isotypes and high affinity antibodies

Naïve T cells

Have not been stimulated by antigen since leaving the thymus

Effector T cells

Have specialized functions e.g. secretion of cytokines or lysis of target cells. Effector cells derive from naïve or memory cells, are short-lived, in an activated state but require further stimulation for full function

Memory T cells

Have had antigen presented to them & return to resting state. They are usually long-lived and can be subsequently reactivated

What are the two signals necessary for T cell activation?

Step 1: Antigen recognition Step 2: Co-stimulatory molecules interact

Co-stimulatory molecules

CD80/CD86 (human) = B7-1/B7-2 (murine = mouse)

Lck

Lymphocyte specific tyrosine kinase

ITAM

Immunoreceptor tyrosine-based activation motif

Clonal Expansion

The second signal results in the proliferation of naïve T cells induced by the production of cytokine, mainly IL-2, which induces proliferation

T cell activation or anergy

MHC/TCR only = anergy ; MHC/TCR + co-stimulation = activation

CTLA-4

If expressed on the T cell, CTLA-4 (inhibitory receptor) can engage CD80/86 instead of CD28. This can also induce anergy

The 3rd Signal

dictates T cell differentiation

T cell functions

Activate macrophages, B cell help/ ab class switching/ affinity, regulate/ inhibit maturation immune responses (tolerance), Produce cytokines, kill infected cells

Activation of CD8+ T cells- cytotoxic T lymphocytes (CTLs)

CD8+ T cells recognize antigen presented by MHC Class I (e.g. virally infected cells)

Cross presentation

The presentation of exogenous antigens on MHC class I Could be viral particles, apoptotic infected cells etc

CD4 Th subset overview

Th1: Inflammatory T cells, produce TNFα/IFNγ, Th2: produce IL-4, IL-5, IL-13 ; Th17: produce IL-17, IL-22 ; Treg: Regulatory T cells – produce IL-10, TGFβ; TFH : Follicular helper T cells – found in 2° lymphoid follicles. This T cell subset are those that activate B cells. Produce IL-4 and IL-21