Helper T Cells - Background

https://www.ncbi.nlm.nih.gov/books/NBK26827/

Introduction

Used in almost all adaptive responses
Activate B cells to secrete Ab and macrophages to destroy microbes
Activate cytotoxic T cells
AIDS lack of helper T cells
Must become effector cells first
Activated on antigen-presenting cells:
- Innate response to infection dictates effector differentiation
- This dictates type of overall immune response

Antigen-Presenting Cells (APC) and Costimulatory Proteins

APC provides 2 signals:
- 1. Foreign peptide bound to protein on cell surface
- 2. Costimulatory proteins (incl B7) induced by pathogens
Effector T cell promote B7 expression yielding positive feedback loop to amplify T cell response

Signal 1 alone causes apoptosis or deactivation (fail-safe to become tolerant to self-antigens). Combined signals differentiate T cell into effector cell by mechanism:

T cell secretes IL-2 causing synthesis of IL-2 receptors
IL-2 binding to IL-2 receptors causes gene switching to induce T-cell differentiating
Safety design so T cells differentiate only when many responding in same location

Binding to APC

Once T cell bound to APC