Introduction to the immune system

Innate (non-adaptive) IS

The first line of defense for the body. Fast response (minutes). No memory

1. Natural barriers to primary infection

2.Antigen non-specific cells - phagocytes (neutrophils, macrophages, dendritic cells)

3.Complement components

4. Inflammatory mediators

Adaptive IS

Very specific! Slow response (days).

Self vs. Nonself

Antigen recognition molecules

Clonal selection

Memory

Pattern recognition receptors

Located on the phagocytic cells (macrophages, neutrophils,dendritic cells). They detect structures commonly found on the surface of bacteria and other pathogens.

Phagocytosis

The ingestion of particulate matter into cells for degradation

Biochemical defenses

1.lysozyme in secretions

2. Sebaceous gland secretions

3. Commensal organisms in the gut and vagina

4. Spearmine in semen

Physical and chemical defenses

1. Coughing and sneezing

2. Mucus and intact mucus membranes

3. Cilia in the trachea

4. Acid in the stomach

5. Dry skin with residual flora

Cytokines

It's messenger molecules that mediate the connection between the two systems (innate and adaptive). The interferons are part of the cytokine family

T and B cells

The effector cells of the adaptive immune system, the white blood cells, the T and B lymphocytes. Normally at rest, but become activated when they meet an antigen.

Epitopes

Small areas of the molecular structures of the foreign antigens

MHC

Major Histocompatibility Complex - it's a group of proteins that are presented on APCs (neutrophils, macrophages, dendritic cells, and B-cells) and demonstrate fragments of antigens to T-cells. It's a bridge between the innate and the adaptive immune systems.

Antigens recognizing molecules

1. B-cell receptors (immunoglobulins or antibodies)

2. TCR

3. MHC (on the APCs)

B-cell and T-cell antigen receptors are clonally distributed. What does this mean?

It means that a unique antigen receptor is found on each lymphocyte.

When a foreign antigen enters the body, it encounters a lymphocyte with a matching receptor.

In case of B cells, the daughter clones produce large amounts of soluble receptor (antibody).

In the case of T cells, large numbers of T cells with a specific antigen receptor on their cell surface are generated.

Whats the difference between BCRs and TCRs

BCR can interact directly with the antigen

TCR recognizes an antigen only when it is presented to them on the surface of another cell by MHC molecules.