1. The Immune System: Adaptive Body Defenses Part B

2. Adaptive (Specific) Defenses - know
The adaptive immune system:
Recognizes specific foreign (non-self) substances
Acts to immobilize, neutralize, or destroy foreign substances
Amplifies inflammatory response and activates complement

3. Adaptive Immune Defenses - know
The adaptive immune system is antigen-specific, systemic (entire body), and has memory
It has two separate but overlapping arms
Humoral, or antibody-mediated immunity (B lymphocytes)
Cellular, or cell-mediated immunity (T lymphocytes)

4. Antigens - know
Substances that can mobilize the immune system and provoke an immune response
The ultimate targets of all immune responses are mostly large, complex molecules not normally found in the body (non-self)

5. Complete Antigens have important functional properties – know definitions, examples
Immunogenicity – the ability to stimulate proliferation of specific lymphocytes and antibody production
Reactivity – the ability to react with the products of the activated lymphocytes and the antibodies released in response to them
Complete antigens include foreign protein, nucleic acid, some lipids, and large polysaccharides

6. Haptens (Incomplete Antigens) – know differences from complete antigens, examples
Small molecules, such as peptides, nucleotides, and many hormones, that are not immunogenic alone but are reactive when attached to protein carriers
If they link up with the body’s proteins, the adaptive immune system may recognize them as foreign and mount a harmful attack (allergy, autoimmunity)
Haptens are found in penicillin, poison ivy, dander, some detergents, and cosmetics

7. Antigenic Determinants - know
Only certain parts of an entire antigen are immunogenic
Antibodies and activated lymphocytes bind to these antigenic determinants
Most naturally occurring antigens have many antigenic determinants that:
Mobilize several different lymphocyte populations
Form different kinds of antibodies against it
Large, chemically simple molecules (e.g., plastics) have little or no immunogenicity

8. Antigenic Determinants - illustration
Figure 21.6

9. Self-Antigens: MHC Proteins - know
Our cells are dotted with protein molecules (self-antigens) that are not antigenic to us but are strongly antigenic to others
One type of these, MHC proteins (Major Histocompatability complex), mark a cell as “self”
The two classes of MHC proteins are:
Class I MHC proteins – found on virtually all body cells bind to T cells
Class II MHC proteins – found on certain cells in the immune response (B cells, macrophages, monocytes and dendritic cells) or “antigen presenting cells”

10. MHC Proteins – know
Are coded for by genes of the major histocompatibility complex (MHC) and are unique to an individual
Each MHC molecule has a deep groove that binds and “displays” a peptide, which is a normal cellular product of protein recycling
In infected cells, MHC proteins bind to fragments of foreign antigens, which play a crucial role in mobilizing the immune system

11. Peptide antigen in MHC groove - understand
Top view
MHC molecule
Peptide

12. Side view, MHC groove - illustration

13. MHC Restriction - know
Antigens (Ag) are recognized as a complex of antigenic peptide and a specific MHC molecule molecule
This co-recognition of peptide and MHC molecule is known as MHC restriction because the MHC molecule is said to “restrict” the ability of the T cell to recognize antigen

14. MHC Restriction – know concept
T cell recognition and activation requires correct combination of antigen + MHC molecule

15. Cells of the Adaptive Immune System - know
Two types of lymphocytes that respond to Ag
B lymphocytes – oversee humoral immunity
T lymphocytes – non-antibody-producing cells that constitute the cell-mediated arm of immunity
Antigen-presenting cells (APCs):
Do not respond to specific antigens
Degrade proteins, bind antigen fragments to MHC molecules, “display” them to T and B cells
Needed to produce a response from a B and T cell

16. B and T Lymphocytes - know
Immature lymphocytes released from bone marrow are essentially identical
Whether a lymphocyte matures into a B cell or a T cell depends on where in the body it becomes “immunocompetent” or “educated” to recognize self vs nonself
B cells mature in the bone marrow
T cells mature in the thymus

17. Antigen-Presenting Cells (APCs) - know
Major rolls in immunity are:
To engulf and degrade particles
To present fragments of antigens on their own surfaces, to be recognized by T cells
Major APCs are dendritic cells (DCs), macrophages, and activated B cells
The major initiators of adaptive immunity are DCs, which actively migrate to the lymph nodes and secondary lymphoid organs and present antigens to T and B cells

18. Macrophages and Dendritic Cells - understand
Secrete soluble proteins that activate T cells
Activated T cells in turn release chemicals that:
“Rev up” the maturation and mobilization of DCs
Cause “resting” macrophages to become “activated” macrophages, which are insatiable phagocytes that secrete bactericidal chemicals

19. Adaptive Immunity: Summary - understand
Defensive system that uses lymphocytes, APCs, and specific molecules to identify and destroy nonself particles
Its response depends upon the ability of its cells to:
Recognize foreign substances (antigens) by binding to them
Communicate with one another so that the whole system mounts a response specific to those antigens

20. Components Of The Immune System

21. Cellular components of the immune system -
illustration
All develop from the pluripotent hematopoietic stem cell.

22. Cellular components - know
The cellular components of the immune system are:
Lymphocytes
Monocytes/Macrophages
Dendritic cells
Granulocytes
Mast cells

23. Cellular components - know
Lymphocytes
- Constitute 20-40% of the white blood cells and 99% of the lymph.
- Lymphocytes are divided into 3 subsets:
a. T lymphocytes ( 60-80% )
b. B Lymphocytes (10-20%)
c. Natural Killer (NK) cells (10%)

24. a. T Lymphocytes - understand
Generated from immature precursors in the
thymus (located in chest, over heart).
- Mature in the thymus, hence they are named
T lymphocytes (T = thymus derived).
- Also found in T-cell zones of the peripheral
lymphoid organs such as the spleen, tonsils and lymph nodes.
- Lymphocytes can be distinguished by their
expression of surface CD (“cluster of
differentiation”) molecules.

25. Lymphocyte
lymphocyte

26. Major Histocompatibility Complex (MHC) - understand
Collection of genes located on chromosome 6 in humans.
Genes codes for 2 major classes of molecules:
i. Class I MHC
ii. Class II MHC

27. Subsets of T cells – know definitions
Based on the expression of surface molecules, T-cells are divided into 2 sub-sets:
CD4 Cells (helper T cells, TH )
CD8 Cells (cytotoxic T cells, TC )
- CD4 molecules bind to MHC II during antigen presentation.
- CD8 molecules bind to MHC I during antigen presentation.

28. T-Cell Receptor Complex - illustration
CD4 T cells bind Class II molecules
CD8 T cells bind Class I molecules

29. How antigens appear on cell surfaces - know
Cells digest proteins into short 5-10 amino acid long peptide antigens
Antigens appear on cell surfaces as combinations of the cell’s own MHC molecules + the peptide
MHC = major histocompatibilty complex molecules
There are two classes of MHC molecules: class I and class II

30. Processing and Presentation of Endogenous
and Viral antigens - illustration
MHC Class I

31. Structure of Class I MHC - understand

32. Processing and Presentation of Exogenous Antigen - illustration
MHC Class II

33. Structure of Class II MHC - understand

34. b. B Lymphocytes - understand
- Develop from immature precursors in the bone marrow, hence the name B lymphocyte.
- Also present in the peripheral lymphoid organs, such as the spleen, lymph nodes, tonsils and extra-lymphatic organs such as gastrointestinal tract.
- Membrane bound Ig immunoglobulins
serve as B-cell receptors.
- Products of B cells are also secreted Ig

35. Structure of an Immunoglobulin (Ig) molecule, also called an antibody molecule - know
Varies, antigen-specific
Same for class of Ig

36. c. Natural Killer (NK) cells - understand
Cytoplasm contains a large number of granules.
Also referred to as Large Granular Lymphocyte.
Do not have receptors for antigen binding on their cell surface.
Can kill tumor cells, virus infected cells without prior sensitization (exposure to them).
Destroy cells based on what they lack instead of what they express