T-Cell and B-Cell Adaptive Responses to Viruses

The adaptive immune response provides antigen-specific control of viral infection and long-lived memory. Cytotoxic CD8 T cells kill virus-infected cells, CD4 helper T cells coordinate and sustain the response, and B cells, with help from follicular helper T cells, mature into antibody-producing plasma cells.

Definition

The adaptive response to viruses is the antigen-specific arm of immunity in which MHC-restricted T cells recognize viral peptides to kill infected cells and provide help, and B cells differentiate into antibody-secreting cells, generating effector responses and durable memory against the virus.

Scope

This entry covers the cellular adaptive response to viruses: antigen presentation by MHC molecules, CD8 cytotoxic T-lymphocyte killing of infected cells, CD4 helper-cell coordination, the germinal-center help that drives antibody responses, and the formation of immunological memory. It is reference material on antiviral immunity rather than clinical guidance; the antibody products themselves are detailed in the humoral-immunity entry.

Core questions

• How are viral antigens processed and presented to T cells by MHC molecules?
• How do cytotoxic CD8 T cells recognize and eliminate infected cells?
• What roles do CD4 helper and follicular helper T cells play in antiviral immunity?
• How does immunological memory form and provide protection on re-exposure?

Key concepts

• Antigen processing and MHC class I and class II presentation
• Cytotoxic CD8 T lymphocytes (CTLs)
• CD4 helper T cells
• Follicular helper T cells and germinal centers
• Effector and memory T-cell differentiation
• Immunological memory

Key theories

MHC restriction

Zinkernagel and Doherty established that virus-specific cytotoxic T cells recognize viral peptide only when presented by self-MHC molecules, defining how T cells detect infected cells.

Mechanisms

Infected and antigen-presenting cells display viral peptides on MHC molecules: endogenously synthesized viral proteins are presented on MHC class I to CD8 T cells, while exogenous antigens are presented on MHC class II to CD4 T cells. CD8 cytotoxic T lymphocytes recognize infected cells through MHC-restricted T-cell receptor engagement and kill them via perforin and granzyme or death-receptor pathways. CD4 helper cells license dendritic cells and sustain CD8 responses, and follicular helper T cells provide the help that drives germinal-center B-cell maturation. After the infection is controlled, a subset of antigen-specific T and B cells persists as long-lived memory that responds faster and more strongly on re-encounter with the virus.

Clinical relevance

T-cell and B-cell responses underlie recovery from many viral infections and the durable protection that vaccines aim to elicit. This entry describes the adaptive antiviral mechanisms and is not a basis for individual diagnostic or treatment decisions.

History

The 1974 discovery of MHC restriction by Zinkernagel and Doherty clarified how T cells recognize virus-infected cells and reframed cellular immunity. Subsequent work resolved antigen-presentation pathways, the differentiation of effector and memory cytotoxic T cells, and the follicular helper T-cell help that drives germinal-center antibody responses, producing an integrated account of antiviral adaptive immunity.

Key figures

• Rolf Zinkernagel
• Peter Doherty
• Michael Bevan
• Antonio Lanzavecchia
• Carola Vinuesa

Seminal works

• zinkernagel-1974
• neefjes-2011
• williams-2007

Frequently asked questions

How do cytotoxic T cells recognize a virus-infected cell?

Infected cells present viral peptides on MHC class I molecules; cytotoxic CD8 T cells whose receptors match that peptide-MHC complex recognize and kill the cell, a property known as MHC restriction.

Why does adaptive immunity provide lasting protection?

After clearing an infection, a subset of antigen-specific T and B cells survives as memory cells that respond faster and more vigorously if the same virus is encountered again.