Chapter 15:Adaptive Immune Response

General Characteristics Involves specialized WBC’s known as lymphocytes Response is highly specific, evolves throughout an organisms life-time Response generates memory Can discriminate between HEALTHY self and non-self OR between HEALTHY self and DAMAGED self

The Adaptive Immune Response Primary response Secondary response Humoral immunity: – B cells, plasma cells, antibodies: target extracellular pathogens Cell-mediated immunity – T cells, dendritic cells – antigen is inside a cell

Overview of the Adaptive Immune Response

Anatomy of the Lymphoid System Lymphatic Vessels Secondary lymphoid Organs Primary Lymphoid Organs

Lymphocytes are responsible for the specific immune response

What promotes an immune response? Antigens – Usually proteins or polysaccharides – Foreign substance with MW of 10,000 daltons – Examples of microbial antigens: bacterial capsules, cell walls, flagella, toxins of bacteria

Antibodies bind antigens

Some molecules are not recognized as antigens until bound to another

How are antigens recognized? Self markers also known as MHC markers MHC (major histocompatibility complex) MHC Class I-produced by all body cells MHC Class II-produced by B cells, T cells, and antigen presenting cells

Structure of an antibody

5 classes of antibodies IgM Produced 1 st Complement activation Primary function = neutralize pathogens in the bloodstream 10 antigen binding sites

5 classes of antibodies IgG Longest half-life Small enough to cross endothelium bbb, some types of placenta Main antibody produced in 2° immune reactions

5 classes of antibodies IgA Monomeric & dimeric Dimer = secretory IgA sIgA = most abundant Ab Secreted across mucosal surfaces in mucus & many other secretions (tears, saliva, milk) Binding → neutralize toxins, block viral and bacterial attachment

5 classes of antibodies IgE Bound to Fc region of mast cells and basophils Cross-linking of IgE by antigen → degranulation

5 classes of antibodies IgD Activation of basophils & mast cells Activation of B cells Highly conserved Functions minimally elucidated

What can happen when antibody binds antigen?

How are B cells activated?

B cell activation by Helper T cell

Primary and secondary response to antigen Affinity maturation Class switching IgM → IgG IgM → IgA Memory B cells+ memory helper T cells: long lived (years)

Helper T cells help activate other immune cells

T cells Have own T cell receptor (TCR) Do not make antibodies Must recognize MHC markers which “present” antigen

MHC markers

Cytotoxic T cells recognize MHC Class I markers

Helper T cells recognize MHC Class II

Dendritic cells can activate T cells

Cytotoxic T cells

Cytotoxic T cells identify infected body cells

Helper T cells activate macrophages

Helper T cells activate B cells

T cell-independent antigens

Antibody-dependent cell-mediated cytotoxicity