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

IgMProduced 1st

Complement activationPrimary function =

neutralize pathogens in the bloodstream

10 antigen binding sites

5 classes of antibodies

IgGLongest half-lifeSmall enough to

cross endothelium bbb, some types of placenta

Main antibody produced in 2° immune reactions

5 classes of antibodiesIgAMonomeric & dimeric

Dimer = secretory IgAsIgA = most abundant AbSecreted across mucosal surfaces

in mucus & many other secretions (tears, saliva, milk)

Binding → neutralize toxins, block viral and bacterial attachment

5 classes of antibodies

IgEBound to Fc region of

mast cells and basophils

Cross-linking of IgE by antigen → degranulation

5 classes of antibodies

IgDActivation of

basophils & mast cells

Activation of B cellsHighly conservedFunctions 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

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