Overview Introduction Humoral immunity is based upon the production and activity of antibodies that login to view 8 more bullets The main effector cell of humoral immunity B-cell that login to view 4 more bullets Humoral immunity occurs in multiple phases including login to view 2 more bullets Activation of Humoral-Mediated Immunity Humoral immunity can be activated by two classes of antigens including login to view 2 more bullets Activation of Humoral Mediated Immunity Feature Thymus Independent Thymus Dependent Function Detect conserved non-peptide antigens Identify pathogens that are missed by T-cells Detect peptide antigens Cooperate with T-cells to clear pathogens Activation steps Crosslinking of B-cell receptors by polymeric antigens Examples include bacterial cell wall or lipopolysaccharide Activation by mitogens to promote general B-cell activity Endocytosis of protein antigens that are detected by the B-cell receptor Processing of these antigens in endosomes and presentation on MHC class 2 Recognition of MHC complexes by activated helper T-cells Interaction of costimulatory CD40 on B-cells with CD40 ligand Differentiation after cytokine stimulation Limitations Does not lead to class switching or affinity maturation Does not produce immunological memory (require adjuvent) Requires peptide antigen Must have functional helper T-cells Affinity Maturation and Isotype Switching After B-cells are activated they can undergo two main processes including login to view 2 more bullets Affinity maturation is a coordinated process with distinct stages including login to view 7 more bullets Isotype switching is stimulated after activation and login to view 8 more bullets Primary and Secondary Responses Upon activation distinct populations of B-cells will develop including login to view 6 more bullets These responses differ in a variety of key aspects Primary versus Secondary Responses Feature Primary Response Secondary Response Function Immediately secrete antibodies Contain infection while secondary response develops Develop into a more effective response with higher affinity Clear infection after development Antibody type Low affinity IgM High affinity IgG IgA in mucosal infections IgE in parasitic infections Timing Early in infection Late in infection