Adaptive immune system

Overview of Adaptive Immune System

  • The adaptive immune system is distinct from the innate immune system, but both systems integrate and interact with each other.

  • Adaptive immunity is also known as learned immunity; it helps the body respond quickly to previously encountered antigens (e.g., bacteria, parasites, viruses).

Antibody Production

  • Antibodies are specific proteins produced in response to particular antigens.

  • These antibodies destroy pathogens directly or link with the complement system to eliminate infected cells.

  • The focus on antibodies highlights the humoral response, a key aspect of adaptive immunity.

Types of Immune Responses

Humoral Response

  • Involves the production of antibodies by B cells, typically occurring in response to pathogens.

  • Activated B cells differentiate into plasma B cells, producing large quantities of antibodies.

Cell-Mediated Response

  • Involves T cells. There are two main types:

    • B Cells: Develop from hematopoietic stem cells in the bone marrow, mature there, and migrate to lymph nodes to produce antibodies when activated.

    • T Cells: Begin development in the bone marrow but mature in the thymus, undergoing a selection process where most fail and only a small percentage mature.

Lymphatic System and Lymph Nodes

  • The lymphatic system collects excess tissue fluid (lymph) and returns it to the bloodstream, maintaining blood fluid balance.

  • Lymph nodes filter this lymph and contain immune cells that help respond to pathogens.

  • Swelling of lymph nodes can indicate infection as immune cells react to pathogens.

Immune Response Activation

  • Upon infection, T cells and B cells in lymph nodes activate in response to pathogens.

  • Cytotoxic T cells (CD8 positive) attack infected or cancerous cells.

  • Helper T cells (CD4 positive) stimulate B cells to produce antibodies and orchestrate the immune response by releasing cytokines (e.g., interleukins).

Immune Response Timeline

  • Adaptive immune response takes about 3-4 days to fully activate after initial exposure to an antigen due to the need to correctly identify and activate T and B cells.

  • Inhibition of unnecessary immune responses prevents autoimmune diseases like rheumatoid arthritis.

Antigen Presenting Cells (APCs)

  • APCs (e.g., macrophages, dendritic cells) process pathogens and present antigens via MHC molecules to T cells to initiate the immune response.

  • This binding is crucial for T cell activation and closely monitored to ensure specificity.

T Cell Activation and Clonal Expansion

  • Activated T cells undergo clonal expansion, producing many identical T cells to rapidly deal with the infection.

  • Memory T cells remain in circulation for quick response if the same antigen is encountered again.

B Cell Activation

  • Activated B cells proliferate and differentiate into plasma cells to produce antibodies specific to the original pathogen.

  • The connection between helper T cells and B cells is crucial for effective antibody production.

Components of Antibodies

  • Antibodies consist of heavy and light chains, with variable regions specific to particular antigens.

  • The variable region allows antibodies to bind to unique epitopes on pathogens.

  • Immunoglobulin Types:

    • IgG: Most abundant and versatile for response against bacteria and viruses.

    • IgM: First antibody type produced in response to infection.

    • IgA, IgD, IgE: Function in various immune roles.

Memory Response

  • Memory B cells remain after an infection, allowing for a quicker response upon re-exposure to the same pathogen.

  • Vaccinations mimic natural exposure to diseases, training the immune system to respond effectively without illness.

Vaccination Strategies

  • Vaccines may use killed pathogens, live attenuated pathogens, or non-infectious toxin derivatives to stimulate immunity without causing disease.