3rd line of defene

• Antigen specific • Memory • Tolerance to self cells • Humoral Response • Cell Mediated Response

• Antigen are components of pathogen that initiates the immune response • Epitope is portion of antigen that is being recognised by lymphocytes to distinguish between pathogens

• B-cells being activated by Helper T cells to produce antibodies • For extracellular pathogens • Release antibodies • RECOGNISE ANTIGENS

• Plasma B-Cell: Produce antibodies • Memory B-Cell: Remain at site of infection in case of reinfection

• For intracellular pathogens • Cytotoxic T-Cell • Helper T-Cell • Memory T-Cell • Suppressor T-Cell

• Secrete cytokines • Release IL-2, B and T Cell activation • Recognise antigens bound to MHC Class 2 molecules

• First time the specific antigen is encountered • Activates T/B Cells

• IgA - Mucosal surfaces, saliva, tears, breastmilk • IgE - Helminths and allergy • IgG - Most common antibody, secreted by plasma cells, can be transferred from mother to infant

• Neutralisation • Agglutination • Precipitation • Compliment System • Opsonisation

• Antibodies binds to antigens to prevent pathogens from entering cells and releasing toxins • Forms Antibody-Antigen Complex

• Antigens binds to multiple antibodies so Antibody-Antigen Complex can aggregate

• Both antigens and antibodies precipitate out of bodily fluids

• Involves T-Cells • Kill intracellular pathogens • RECOGNISE EPITOPE

• MHC Class 1 is found on all nucleated cells and activates Cytotoxic T-Cells • MHC Class 2 is found on antigen-presenting cells and activates Helper T-Cell