Adaptive Immunity Overview

Adaptive Immunity

• Adaptive immunity is a specialized immune response that targets specific pathogens
• Adaptive immunity involves two fundamental topics in biology
• The adaptive immune system is characterized by its ability to respond to specific pathogens and to develop immunological memory

Cells of the Adaptive Immune System

• The main cells involved are CD4 T cells, CD8 T cells, and B cells
• These specialized cells work together to rid the body of pathogens

Adaptive Immunity Activation

• The adaptive immune system is activated in secondary lymphoid organs, such as lymph nodes and spleen
• Antigens are processed and presented to T cells by antigen-presenting cells (APCs), like dendritic cells
• The activation of T cells requires three signals including costimulation
• B cells are activated by binding to native antigens in their B cell receptors (BCRs)

Cellular Immunity

• Pathogens infect tissues
• Activated dendritic cells (DCs) migrate to lymphoid organs carrying the pathogen
• DCs activate antigen-specific T cells
• T cells proliferate, and some migrate out of the lymph node and become effector T cells
• The effector T cells migrate to infected tissues to clear the infection
• T and B cell activation takes place in secondary lymphoid organs
• Paracortex or T cell zone: where DCs from the tissue meet naïve CD4 and CD8 T cells
• Dendritic cells enter lymph nodes through afferent lymphatic vessels
• B cell follicles: where B cells are found and respond to antigen

T Cell Activation

• T cells require continued activation and sustained differentiation signals
• T-cell recognition involves the interaction of a TCR with an antigen presented on an MHC molecule
• The adaptive immune system is essential for recognizing specific pathogens and developing immunological memory

B Cell Activation

• B cells recognize native proteins or antigens with their B cell receptors (BCRs)
• Antigens that cross-link surface BCRs are optimal for B cell activation
• B cell activation does not require accessory cells
• Smaller antigens and pathogen products drain into lymph nodes
• Dendritic cells carry antigens and pathogens to the lymph node and pass them to B cells
• Smaller antigens are often picked up by macrophages and passed to B cells

B and T Cell Activation

• Some activated CD4 T cells move toward the B cell follicle
• Activated B cells move toward the T cell zone and present peptides from the pathogen on MHCII to activated CD4 T cells
• The T and B cells move together to form a germinal center
• The cells in the germinal center are call T follicular helper (Tfh) cells

Antibody Production

• B cells differentiate into plasma cells which produce antibodies
• The B cell receptors (BCRs) undergo somatic hypermutation and class switching in the germinal center
• Class switching leads to diverse antibody types, such as IgM, IgG, IgE, and IgA
• Antibodies play a role in neutralizing pathogens, activating complement, and enhancing phagocytosis

Cell Response

• Most T and B cells undergo apoptosis after infection or vaccination
• Some cells remain as memory cells, providing a rapid response to future encounters with the same pathogen
• We take advantage of the functions of memory cells during vaccination

Related Concepts

• Pathogens activate DCs to present antigen to T cells; a concept linked to the "Sensing Danger" lecture
• Knowledge of the adaptive immune system is used to improve vaccines; related to the "Vaccination: design and mechanisms" lecture

Explore the crucial concepts of adaptive immunity, including its specialized immune responses, main cellular players, and activation processes. Understand how CD4 T cells, CD8 T cells, and B cells collaborate to combat pathogens and establish immunological memory. This quiz will test your knowledge on the roles of these immune cells and their activation in lymphoid organs.