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

TC (Cytotoxic T cells)

TH (Helper T cells)

Also function in immune system

Origins of lymphocytes

B cell activation and differentiation

Origins of lymphocytes

T cell activation

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 ComplementAdaptive 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

Heavy chain constant region determines antibody class

N

C

N

C

B cell development

B cell development

Heavy chain gene rearrangement

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 possibleantigen binding sites from gene segment combinations

IgM IgD IgG IgE IgA

B cell development

Light chain gene rearrangement

Human light-chain gene rearrangement

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

(stops gene rearrangements)

Clonal selection

Memory cells:

Somatic hypermutation in V regions

Class switching

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 possibleantigen binding sites from gene segment combinations

IgM IgD IgG IgE IgA

Rearrangements in memory cells can put a different C region gene segment in register, thereby causing antibody class switching