Biology 318Specific Host Defenses

Lines of Defense• First - non-specific (NS)

barriers, normal flora• Second - NS immune

cells, proteins, processes

• Third - specific immune cells and antibodies

Properties of Immune system

• Recognize foreign molecules

• Recognize self• On –off

Lymphocyte editing

• Clonal deletion• Reduce autoimmune response• Major histocompatability complexes (MHC),

located on chromosome 6• Class I: on all nucealated cells• Class II: B lymphocytes and Antigen presenting

cells (APC)• Determine which cells trigger immune response

Two major branches of the immune system

Antigens (Ag)

Any agent that stimulates third line defensesOne Ag = many determinants (surface shapes)Each is RECOGNIZED and MEMORIZEDHaptens: small molecules on a large carrier molecules

(Penicillin)

Lymphatic system

• Lymph vessels• Ducts• Red bone marrow• Thymus gland• Spleen• Tonsils• MALT (mucosa

associated lymph tissue)

Humoral immunity: Specific B-Cells (lymphocytes)

Made in bone marrow, develop in liver and GI

Secrete antibody proteins specific to antigens

Kinds of B-cells – plasma and memory

Blood Antibodies made -IgM and IgG

None circulate unless activated by Helper-T.

Basic Antibody structure

Antibodies - What They Do

Opsonization: Activate complement and recruit phagocytes

Agglutinate (clump) MANY AgNeutralize Ag effects (e.g. halt toxins)

Be sure you FULLY understand IgG, M, and A.

Antibodies

Humoral Response Chain of Command

• Ag digested into bits by phagocyte

• Phagocyte presents bits to Helper-T

• Helper-T finds right B-cell (1/100,000,000)

• Chosen B-cell divides -plasma and memory

• IgM first exposure; IgGsecond - BOTH lifelong

• Memory cells - retained for future reference

Cell-Meditated: Specific T-Cells (lymphocytes)

Made in bone marrow, develop in thymus

Express surface proteins specific to Ag

Kinds – helper, killer, suppressors, memory…

Helpers circulate at all times - others must be activated during blood exposure.

Cell-Mediated - Chain of Command

Same as Humoral through Helper-THelper-T finds right T-cell (1/100,000,000)Chosen T-cell divides into:

Cytotoxic – actively kill AgSuppressor – eventually stops killing Memory - retained for future reference

The AMAZING Numbers100,000,000 different B-cells and antibodies100,000,000 different T-cells surface proteins

Not everyone has 100,000,000 - implications?

Mucosal Lymphocytes Embedded in epithelium - poorly understoodSecrete IgA antibodies - last only 3-6 monthsNon-blood Ag recognized by these specific cellsThat’s why you catch some things many times