Adaptive immunity How can the immune system recognize so many different (previously unseen) insults? How does the immune system learn? How do B cells produce antibodies?

Antibody production after immunization

Irradiation prevents immune response

Which cells can restore the immune response?

Origins of lymphocytes

B cells T C (Cytotoxic T cells) T H (Helper T cells) Also function in immune system

Origins of lymphocytes

Antibody protein structure

B cell activation Each naïve B cell makes a single type of antibody with a unique binding specificity Upon activation the naïve B cell proliferates and produces progeny that secrete that antibody

Antibody production after immunization

Clonal selection

Primary response Secondary response

Antibody action: Activation of Complement Adaptive immunity (Innate immunity)

Antibody action: Action of Complement

Antibody action: IgG-mediated phagocytosis

Antibody action: IgA is secreted

Antibody action: IgE stimulates histamine production

Antibody structure Determines antibody class

Human heavy chain gene-segment pool 51 x 27 x 6 = 8262 possible H chain variable regions 40 x 5 = 200 possible  light chain variable regions 116 possible chain variable regions 2.6 million possible antigen binding sites from gene segment combinations IgM IgG IgD IgE IgA

Human heavy chain gene-segment pool 51 x 27 x 6 = 8262 possible H chain variable regions 40 x 5 = 200 possible  light chain variable regions 116 possible chain variable regions 2.6 million possible antigen binding sites from gene segment combinations

Human  light- chain gene rearrangement

Ab gene usage in a pre-B cell (allelic exclusion)

Clonal selection

Memory cells: Somatic hypermutation in V regions Class switching