5.10 humoral adaptive immunity & B lymphocytes

humoral vs cell mediated immunity (target)

humoral immunity acts primarily against extracellular pathogens

cell mediated immunity acts primarily against intracellular pathogens

plasma B cells

secrete antibodies specific to the infection, each plasma cell can only produce one type of antibody, short lived

memory B cells

remain in the lymphatic tissue to remember the antigen for future infections

clonal selection in B cells

APCs display foreign antigens on their MHC-II markers and bind to specific complementary cells in the lymph nodes

clonal expansion in B cells

the differentiation and proliferation of B cells into plasma cells and memory B cells

steps in activation of humoral adaptive immunity

1. B cells undergo clonal selection

2. helper T cells that bind to the antigen release cytokines (interleukin) to activate specific B cells

3. B cells undergo clonal expansion (activated by clonal selection and helper T cells)

4. plasma cells and memory B cells are produced

antibody structure

• constant regions

• variable region (antigen-binding site)

• light & heavy chains

• quaternary structure

• both sides identical

antibody function

• precipitation

• inflammation

• agglutination

• neutralisation (of pathogens and toxins)

• opsonisation

precipitation

• antibodies bind to soluble antigens, making them insoluble

• causes antigens to precipitate out of solution, creating a solid more visible to the IS

• occurs due to cross-linking between antigens and antibodies

inflammation

• antibodies can trigger the release of histamine, causing inflammation

• can also activate a complement cascade

agglutination

• antibodies bind to surface antigens on pathogens to form antigen-antibody complexes

• causes pathogens to clump together and become more visible to the IS

neutralisation (of pathogens and toxins)

• antibodies bind to toxins, venoms and surface antigens on pathogens, neutralising them via a coating and preventing them from binding to cell surface receptors

opsonisation

• antibodies bind to surface antigens on pathogens to form antigen-antibody complexes and tag the pathogen for destruction

• activates phagocytes and complement proteins, leading to the pathogen’s destruction