Adaptive Immunity

1. Vertebrates only

2. Specificity- recognition modules - BCR, Ab and TCR- gene rearrangement is the source of diversity- clonal selection

3. Small lymphocytes- types and sub-types- functions

Recognition concept

Receptor or Antibody molecule

Antigen - structure recognized by an Ab, BCR or TCR

Epitope - particular sub-structure of the Ag that is bound

Affinity - how much a molecule likes to bind to a structure

B-cellsBCR is Immunoglobulin (Ig)Plasma cells - effector cells that secrete Ab

T-cellsTc = cytotoxic (CD8+)

TH = helper T-cells (CD4+)Th1 (inflammation)Th2 (help B-cells make AB)

Small lymphocyte sub-types

Recognition modules of Adaptive immunity

B cells T cells

B-cell receptor

B-cells T-cell

Native vs Denatured

Antigen processing

Major Histocomp-atibility (MHC)

How does MHC work?

Intracellularpathogens

All nucleated cellsAPC

Extracellular pathogens

Only immune cellsProfessional APC

APC - Antigen Presenting Cells

Professional APC- macrophages- B cells- Dendritic cells

Figure 1-26MHC class I communicates with Tc cells

Figure 1-27MHC class II communicates with TH cells

Dendritic cells interact with naïve T-cells and initiate differentiation

How do Antibodies work?

Parasite +

Mast cell

Inflammation

Mast cell activated

Expel and/or destroy

pathogen

• Neutralization• Opsonization• Inflammation

Parasitic infection

Principles of Adaptive Immunity

DiversitySpecificityMemorySelf-tolerance

Gene Rearrangement is the source of Diversity

Germline configuration

Diversity1. Alternative combinations2. Imprecise joints3. Different types of chains4. B-cells - somatic hypermutation

In the absence of antigen

Clonal Selection

1. Each cell = one receptor2. Millions of lymphocytes

are generated3. Small subset will

recognize a pathogen4. Proliferation and

differentiation5. Acquired immunity - the

adaptive immunity provided by immunological memory

Figure 1-22Antibodies are usually very specific

Figure 1-30

Few specific lymphocytes

Many lymphocytes

Some memory lymphocytes

Concept Behind Vaccination

•Pre-industrialization infants built immunity naturally

•Post-industrialization polio rate increased in adults hence a need for vaccination

Polio Vaccine - Inactive vs Oral “live” version

VDPV - vaccine derived polio virus- mutations can lead to polio at extremely low rate

Principle of Self-tolerance

B-cells with BCR that bind to self will undergo Apoptosis

More complicated scheme of selection for T cells

Mechanism of Self-tolerance

Selection of T cells

1. Thymocytes

2. Positive selection-Self MHC

3. Negative selection

Immunodeficiencies

Inherited deficienciese.g. Bubble boy disease

Stress induced nutrition, emotional

Pathogen caused deficienciesHIV - attacks CD4 T lymphocyte

Figure 1-32

• IgE

• IgG

• CD4 TH1

• CD8 CTL

Cells and molecules involved in Hypersensitivity Diseases

Figure 1-33Insulin-Dependent Diabetes Mellitus

Beta cells of the Islets of Langerhans

Figure 1-34

Hygiene Hypothesis

Inflammatory Adaptive Immune Response