Introduction to The Immune Response Dr. Robert J. Boackle Room 441 BSB,

The Student should understand the following concepts from this lecture:  The Nature of Antigenic Determinants  Location of Antigens on Bacterial Cells  After infection, the Filtration of Antigens  Lymphocyte Clones (B Cells and T Cells)  B and T Lymphocyte Clonal Development  B and T Lymphocyte Clonal Proliferation  Lymphocyte Circulation and Trafficking

Non-self Substances Antigens [Ag]

Where are antigens located? Lets take a look at the molecular level. Bacterium

Released Antigens Surface Antigens Bacterial Surface

Released Proteases Surface Antigens Bacterial Surface

Bacterial Proteases play a key role in Periodontal Disease unless they are neutralized by host antibodies

Bacterium Antigens are foreign molecules

Each Antigen (each foreign molecule) (for example a bacterial surface enzyme) has several regions that our body detects as foreign. These areas on the molecule are termed Antigenic Determinants

X EXTERNAL THERE ARE ALSO MANY INTERNAL ANTIGENIC DETERMINANTS (not exposed) Activate T Cells EXTERNAL ANTIGENIC DETERMINANTS Activate B Cells

Antigen Penetration

Toll-like Receptors Endotoxin (LPS)

VEIN ARTERY LYMPH NODE EFFERENT LYMPHATIC CAPILLARY AFFERENT LYMPHATIC CAPILLARY

VEIN ARTERY EFFERENT LYMPHATIC CAPILLARY Antigens in the Lymph are filtered in the Lymph Node

AL = AFFERENT LYMPHATIC CAPILLARIES AL B CELL RICH T CELL RICH AL EFFERENT..LYMPHATIC..CAPILLARY Antigen Stimulated Lymph Node Lymph Node Lymphocyte Proliferation Swollen Lymph Nodes ! Movement of Lymphocytes from “Blood to Lymph” occurs in the Lymph Nodes

Antigens in the Blood are filtered in the Spleen Spleen

LymphocytesLymphocytes are the police force of the Immune System These Lymphocytes are the detectives and responders They traffic to areas of infection and inflammation! Selectins- Integrins Addressins

Location of Lymphocytes: Lymph and Lymph Nodes Blood and Spleen Thymus Bone Marrow Lymphoid Tissues Associated with the Mucosa (Tonsils, Gut, Respiratory Tract) Any area after infection

Regulation of the Expression of DNA is the key to the production of different kinds of Lymphocytes And to the understanding of Lymphocyte Clonal Development The ability of a population of Lymphocytes to SPECIFICALLY recognize a foreign antigen

1) One Clone of B Lymphocytes is a population of B lymphocytes derived from one original mother B lymphocyte and therefore all members are identical in every way. 2) One Clone of T Lymphocytes is a population of T lymphocytes derived from one original mother T lymphocyte and therefore all members are identical in every way. Definitions:

3) There are thousands of B cell clones and thousands of T cell clones in our body that exist in low numbers until we have an infection. 4)Stem cells are pre-programmed with the DNA-information to generate thousands of different clones of B and T lymphocytes (to bind to thousands of different antigenic determinants). 5)An Antigenic Determinant adheres to the best fitting Clone of B or T Lymphocytes. Definitions:

B Lymphocyte Clonal Development STEM CELLS in the BONE MARROW are pre-programmed with information BONE MARROW Clones of B Cells are formed within the Bone Marrow of humans No Antigen Needed!

Mature B lymphocytes divide very slowly in the absence of antigens BL

What are the Lymphocyte Receptors for antigenic determinants integrated with the membranes of lymphocytes? For B lymphocytes the Receptors are Antibodies For T lymphocytes the Receptors are T Cell Receptors

IN THE PRESENCE OF ANTIGENS, Clonal Proliferation (B Cell clonal expansion), followed by Differentiation into Plasma cells that produce identical fluid phase antibodies (Ab)

What do we mean by the phrase “Clones of Lymphocytes”

Only those lymphocyte clones that bind in a specific way to antigens are stimulated.

Clones of B and T Lymphocytes (inactive) Clonal Selection Theory

Selected Clones of B Lymphocytes and T Lymphocytes Activate and Proliferate After contacting antigens

Clones of B Lymphocytes become activated by exposed antigenic determinants on antigens Clonal Selection Theory Clone B1 Clone B2 Clone B 3 And Proliferate

Proliferation of ONE B Cell Clone after contacting antigen. Clonal Proliferation after binding to one exposed antigenic determinant on antigens. Clonal Expansion ( Memory Cells) Clone ExpandMORE Expand

X EXTERNAL EXTERNAL ANTIGENIC DETERMINANTS bind to Specific B Lymphocyte Clones

B lymphocytes interact with an exposed antigenic determinant via antibody-receptors on their surface. All cells in this “clone” of B lymphocytes (BL) produce antibodies on their surface that interact with only one type of Antigenic Determinant. Antigen

Antigenic Determinant Antibody On the B cell surface The Antigen

One antigenic molecule may have several different Exposed ANTIGENIC DETERMINANTS Example of Three (exposed) Antigenic Determinants on this foreign protein.

A Separate Antibody Response results (at the same time) to each of these exposed antigenic determinants on this one antigenic molecule B cell Clone # 1B cell Clone # 2B cell Clone # 3

We term these B Cell Host Responses and the resulting production of Specific Antibody Responses as Humoral (Fluid) Immunity

Humoral Immunity BL + Exposed Antigenic Determinant Specific Clonal Response

So how large must an antigenic determinant be to be “seen” by a B Lymphocyte? B lymphocytes interact with exposed antigenic determinants via the antibody receptors they produce on their surface.

Exposed Antigenic Determinants are Comprised of at least Five to Six amino acids

For B cell antibody, Each Antigenic Site (Determinant) is a function of 1) Non-Identity with any Host Substance 2) Outside Molecular Exposure outside charges and its conformation (must fit into the specific binding site of Antibody) Antigenic Determinant Antibody On the B cell surface Rest of the Antigen Now the -- B Cell may become activated

One clone of B lymphocytes is activated by One Antigenic Determinant Clone 1 Clone 2 Clone 3

2,000 Antibodies per second per plasma cell Live only two or three days

The clones of B Lymphocytes that bind with the highest affinity to the antigenic determinant are stimulated the most

Now we will discuss T lymphocytes

T Lymphocyte Clonal Diversification is in the Thymus & And occurs in the Absence of foreign antigens

STEM CELLS from the THYMUS T Lymphocyte Clonal Diversification in the Thymus A lot of dividing & living and a lot of dying (no foreign antigens needed in the Thymus)

STEM CELLS from the Mature T Lymphocytes Produced (no foreign antigens were needed) T T T

STEM CELLS from the In Pregnant Women X-rays are forbidden because there is no time for DNA repair in rapidly dividing cells.

T lymphocytes divide slowly in the absence of antigens and may live for years TL

T Cell Receptors are the T Lymphocyte’s Receptors for antigens (Not antibodies) TL

Processed antigenic determinants cause the Proliferation of this Specific T cell clone TL This T Cell does not bind to this antigenic determinant and so is not activated TL

Processed antigenic determinants cause the Proliferation of this Specific T cell clone TL

T Lymphocytes “Cell Mediated Immunity”

Clones of T Lymphocytes become activated by different (internal) antigenic determinants (fragments) Clonal Selection Theory Clone T1 Clone T2 Clone T 3 And Proliferate

Upon activation, each of the activated clones expands. That is, the cells in that clone divide and multiply. “PROLIFERATION”

Example of the location of Proliferating B and T Cell Clones inLymphNodes.pdf

From Your Textbook on page 14

“The Selectins mediate transient interactions between leukocytes and endothelial cells or blood platelets. There are three members of the selectin family: L-selectin, which is expressed on leukocytes; E-selectin, which is expressed on endothelial cells; and P-selectin, which is expressed on platelets. The selectins recognize cell surface carbohydrates. One of their critical roles is to initiate the interactions between leukocytes and endothelial cells during the migration of leukocytes from the circulation to sites of tissue inflammation. The selectins mediate the initial adhesion of leukocytes to endothelial cells. This is followed by the formation of more stable adhesions, in which integrins on the surface of leukocytes bind to intercellular adhesion molecules (ICAMs), which are members of the Ig superfamily expressed on the surface of endothelial cells. The firmly attached leukocytes are then able to penetrate the walls of capillaries and enter the underlying tissue by migrating between endothelial cells.” Quoted from Selectins-Integrins AddressinsSelectins-Integrins Addressins Please see

1)Any one lymphocyte has only one type of receptor (>10,000 receptors per cell) and each of those receptors on its surface are all identical in every way (including binding to one specific type of antigenic determinant). 2)Each cell in a Clone is identical in every way. Therefore, all the receptors on the cells that comprise a clone have the same affinity for a particular antigenic determinant. Important Definitions:

The T Cell Receptors are all identical on every cell in a clone of T Cells The T Cell Receptors do not interact with exposed antigens like antibodies do on B lymphocytes. Rather T Cell Receptors detect internal (previously hidden) antigenic determinants that must be processed (e.g., digested or fabricated) by other cells and then presented to the T Lymphocytes in the correct way.

Cell Mediated Immunity TL + Processed Antigenic Determinant Specific T Cell Clonal Response

ACTIVATED T CELLS LIBERATE BIOLOGICALLY ACTIVE MOLECULES TL CYTOKINESCYTOKINES INTERLEUKINSINTERLEUKINS Presented antigenic determinant

Chemotactic Molecules (Interleukins)

Circulation of Lymphocytes

Circulation of Lymphocytes from Blood to Lymph (after binding to the Peripheral Lymph Node Addressin molecules on the Postcapillary High Endothelial Venules in the Lymph Nodes), then from Lymph back to Blood via the Thoracic Duct Lymph Node Circulating Policemen Peripheral Lymph Node Addressin Peripheral Lymph Node Addressin PNAd is on the

Berg EL, Robinson MK, Warnock RA, Butcher EC. J Cell Biol. 1991, 114:: The human peripheral lymph node vascular addressin called PNAd, is a ligand for LECAM-1, the peripheral lymph node homing receptor. The trafficking of lymphocytes from the blood into lymphoid organs is controlled by tissue-selective lymphocyte interactions with specialized endothelial cells lining post capillary venules, in particular the high endothelial venules (HEV) found in lymphoid tissues and sites of chronic inflammation. Lymphocyte interactions with HEV are mediated in part by these lymphocyte homing receptors and tissue-specific HEV determinants, the vascular addressins. PNAd is molecularly distinct from the mucosal vascular addressin termed MAdCAM-1.

Circulation of Lymphocytes from Blood to Lymph (in the Peyer’s patches) The mucosal vascular addressin termed MAdCAM-1 and the PNAd are found on venules feeding mucosal lymphoid tissues such as the Payer’s Patches

Briskin MJ, McEvoy LM, Butcher EC. Nature. 1993, 363: Tissue-specific homing of lymphocytes to mucosal tissues The mucosal vascular addressin ( MAdCAM-1) is selectively expressed on high endothelial venules (HEV) of mucosal lymphoid organ and on lamina propria venules and helps direct lymphocyte traffic, (such as IgA committed B cells) to these mucosal tissues.

Circulation of Lymphocytes in Blood (through the Spleen)

After the host has generated an Immune Response to Antigens, then we state that those Antigens were Immunogenic