Pathogens that cannot be handled by innate immunity are dealt with by adaptive immunity, which specializes in specific targets. One type is humoral immunity, in which antibodies play the main role.
Basic Knowledge
The main cells of adaptive immunity are the lymphocytes called B cells and T cells. Of the lymphocytes born in the bone marrow, B cells mature in the bone marrow, while T cells mature in the thymus.
Process of humoral immunity:
① Dendritic cells take in pathogens and present their antigens to helper T cells in the lymph nodes.
② Helper T cells become activated and cause the corresponding B cells to proliferate and differentiate.
③ B cells differentiate into plasma cells and produce and release large amounts of antibodies(immunoglobulins).
④ Antibodies bind to antigens and cause an antigen-antibody reaction, neutralizing pathogens or making them easier for phagocytes to eat(opsonization).
Antibodies are Y-shaped proteins, and their terminal variable regions bind specifically to antigens.
Adaptive immunity（Immunity that responds specifically to particular antigens; carried out by lymphocytes）
Antigen（A foreign substance that causes an immune response, such as a pathogen or protein）
B cells（Mature in the bone marrow; differentiate into antibody-producing cells）
Helper T cells（Mature in the thymus; activate B cells and other T cells）
Antibodies（immunoglobulins）（Y-shaped proteins that bind to antigens with their variable regions）
Antigen-antibody reaction（A reaction in which an antigen and antibody bind specifically）
Plasma cells（Antibody-producing cells differentiated from activated B cells）
Further Study
Antibodies are remarkable molecules capable of producing an unlimited variety. Genes for their variable regions are combined through gene rearrangement(V-D-J rearrangement), and it is thought that one person can produce more than 1 billion different antibodies. Shin'ya Tonegawa of MIT received the Nobel Prize in Physiology or Medicine in 1987 for this discovery.
Antibodies have various functions beyond simply “binding”: ① neutralization, which removes a pathogen's ability to infect; ② opsonization, which makes pathogens easier for phagocytes to eat; and ③ agglutination, in which multiple antibodies and complement link together and gather pathogens. These functions work together to eliminate pathogens.
- Main cells of adaptive immunity=B cells・T cells(lymphocytes)
- B cells=mature in bone marrow, T cells=mature in thymus
- Humoral immunity=immunity based on antibodies
- Antibodies=immunoglobulins(Y-shaped proteins)
- Antigen presentation by dendritic cells→helper T cells→B-cell activation
- Plasma cells produce large amounts of antibodies
- Antigen-antibody reactions neutralize・agglutinate・opsonize pathogens
Points to Note
① Never confuse an antigen(the foreign substance itself) with an antibody(the protein that binds to the antigen). ② The “B” in B cell comes from bone marrow, and the “T” in T cell comes from thymus. ③ Antibodies are not produced by B cells themselves but by differentiated plasma cells. ④ Humoral immunity is immunity through fluid components(antibodies), whereas the cell-mediated immunity studied next is immunity in which T cells themselves attack; they are different.
Practice
- What type of cell do B cells differentiate into to produce antibodies?
- Which organ is where T cells mature?
- What is the part of the Y-shaped antibody structure that binds to an antigen called?