Essentials of Biology Sylvia S. Mader Chapter 26 Lecture Outline Prepared by: Dr. Stephen Ebbs Southern Illinois University Carbondale Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

26.1 Organs, Tissues, and Cells of the Immune System The immune system protects the body by fighting infection and cancer. The immune systems consists of several lymphatic organs. – Red bone marrow – Thymus gland – Lymph nodes – Spleen

26.1 Organs, Tissues, and Cells of the Immune System (cont.) There are also specialized lymphatic tissues. – Tonsils – Appendix Specialized cells also contribute to the immune system.

26.1 Organs, Tissues, and Cells of the Immune System (cont.)

26.1 Organs, Tissues, and Cells of the Immune System (cont.)

26.1 Organs, Tissues, and Cells of the Immune System (cont.) These various organs, tissues, and cells provide for immunity, which is the ability to react to antigens. Antigens are proteins that are foreign to the organism. • Antibodies are specialized proteins produced by an organism that bind to specific antigens.

Lymphatic Organs Each lymphatic organ has a specific function in immunity. All lymphatic organs contains one or more lymphocytes, one category of immunocells that protect the body.

Red Bone Marrow The red bone marrow produces all the different types of red blood cells. There are several types of lymphocytes produced by the red bone marrow. – B lymphocytes, also called B cells – T lymphocytes, also called T cells

Thymus Gland Immature T cells produced by the red bone marrow migrate to the thymus where they complete their maturation. The thymus produces hormones that are thought to help T cells mature. The thymus selectively release T cells that have matured properly.

Lymph Nodes The lymph nodes filter the lymphatic fluid to remove antigens and pathogens. Antigens and pathogens are removed by the phagocytic macrophages. Lymphocytes in the lymph nodes all contribute to the defense against antigens and pathogens in the lymphatic fluid.

Spleen The spleen has two areas that contribute to immunity. – Red pulp – White pulp The red pulp filters pathogens and debris with the help of macrophages. The white pulp contains lymphocytes that fight pathogens and cancer.

26.2 Nonspecific Defenses The body has a variety of nonspecific defenses that help protect the body from infection. Barriers to entry The inflammatory response Natural killer cells

Barriers to Entry There are two primary barriers that prevent entry of pathogens into the body. The skin The mucous membranes In addition to mechanically blocking pathogen entry, the skin has oil glands secrete chemicals to counter pathogens.

Barriers to Entry (cont.)

The Inflammatory Response Any damage to the body’s tissues trigger events of the inflammatory response. Reddening An increase in temperature Swelling Pain The inflammatory response also involves three cell types. – Mast cells – Neutrophils – Macrophages

The Inflammatory Response (cont.) The mast cells release chemicals such as histamine to increase the blood flow through the capillaries. This increased blood flow contributes to the redness, swelling, and warmth. Because of the swelling, nerve receptors are triggered to create the sensation of pain.

The Inflammatory Response (cont.) • Neutrophils are phagocytic white blood cells that migrate to the site of injury. Macrophages have several roles. These cells are phagocytic. These cells release chemicals that trigger white blood cell production in the red marrow.

The Inflammatory Response (cont.)

The Inflammatory Response (cont.)

The Complement System The complement system consists of a variety of blood plasma proteins. When activated by the presence of pathogens, these proteins amplify the immune response. Complement proteins also form a membrane attack complex that contributes to the lysis of pathogens.

The Complement System (cont.)

Natural Killer Cells • Natural killer cells are non-specific lymphocytes that kill virus-infected and cancerous cells. Natural killer cells kills cells that lack surface proteins identifying them as “self”.

26.3 Specific Defenses • Specific defenses are used in immunity when the nonspecific defenses fail to halt a pathogen or infection. One advantage of the specific defenses is that they can provide a “memory” of the infection.

B Cells and the Antibody Response The B-cell receptor (BCR) on the surface of B cells allows for the recognition of and binding to specific antigens. The binding of the BCR to an antigen activates the B cell. Activated B cells undergo cell division to produce two special types of B cells. – Plasma B cells – Memory B cells

B Cells and the Antibody Response (cont.) • Plasma cells are responsible for the mass production of antibodies for the antigen. The antibodies are released into the bloodstream to help the body identify the antigen within the body.

B Cells and the Antibody Response (cont.)

B Cells and the Antibody Response (cont.) • Memory B cells are retained within the body for an extended period of time. The memory B cells allow the body to mount an immune response more quickly if the antigen is perceived again.

B Cells and the Antibody Response (cont.)

The Function of Antibodies Recall that antibodies are immunoglobulin proteins that recognize specific antigens and forms an antibody-antigen complex. The formation of an antibody-antigen complex can mark an antigen for destruction by neutrophils or macrophages. The antibody-antigen complex may also act as complement to amplify the immune response.

The Function of Antibodies (cont.)

The Function of Antibodies (cont.) The proteins that determine blood type are also a type of antigen on the surface of red blood cells. Type A, B, or AB blood results from the presence of the A and/or B antigen. Type O blood occurs when the red blood cells lack the A or B antigen.

The Function of Antibodies (cont.) The blood also contains antibodies to the red blood cell antigens that are not present. If incompatible types of blood are mixed, antibody-antigen complexes can form when agglutination occurs. This clumping of red blood cells restricts blood flow and can ultimately be fatal.

The Function of Antibodies (cont.)

T Cells and the Cellular Response The mature T cells that leave the thymus gland have unique T-cell receptors (TCR). These receptors only recognize an antigen when an antigen-presenting complex (APC) of a macrophage presents the antigen to the TCR. The presentation of the antigen by the APC activates the T cell.

T Cells and the Cellular Response (cont.) An activated T cell undergoes cell division to produce two types of T cells. – Cytotoxic T cells – Helper T cells

T Cells and the Cellular Response (cont.)

Types of T Cells • Cytotoxic T cells release a protein called perforin to create a pore in the surface of infected cells. Cytotoxic T cells also release granzymes that then trigger the infected cell to undergo apoptosis (self-destruct). Cytotoxic T cells are responsible for the response to virus-infected and cancerous cells.

Types of T Cells (cont.)

Types of T Cells (cont.)

Types of T Cells (cont.) • Helper T cells contribute to immunity by secreting cytokines. Cytokines are chemicals that stimulate the immunocells, particularly the B cells.

Tissue Rejection The immune system may also be important when an individual receives an organ transplant. • Rejection occurs when cytotoxic T cells and antibodies respond to the transplanted tissues as if they were pathogens. Tissue rejection can be minimized in two ways. Transplanting tissues with similar surface antigens to the recipient. Administering immunosuppressing drugs.

26.4 Immunizations • Vaccines and immunizations are used to protect individuals from specific diseases. The introduction of a vaccine promotes an active immune response and the formation of memory B cells. This acquired immunity prepares the body to respond quickly if the disease is perceived again.

26.4 Immunizations (cont.)

26.4 Immunizations (cont.) Temporary immunity can also be imposed through the introduction of specific prepared antibodies to the body. This immunity is passive immunity. Another example of passive immunity is the transfer of antibodies from mother to child during breast-feeding.

26.5 Immune System Problems The immune system itself can malfunction and become harmful to the body. This can occur when the immune system fails to distinguish “self” from “nonself”.

Allergies • Allergies are a hypersensitive response to antigens called allergens. An immediate allergic response occurs within seconds of exposure to an allergen and may be life-threatening. The immediate allergic response involves the release of histamine from mast cells.

Allergies (cont.) • Delayed allergic responses occur at point after the exposure to the allergen. The delayed response is probably due to the cytokines secreted by immunocells.

Allergies (cont.)

Autoimmune Diseases • Autoimmune diseases occur when cytotoxic T cells attack the body’s own cells. There are several autoimmune diseases. Multiple sclerosis Systemic lupus Rheumatoid arthritis

AIDS • Acquired immunodeficiency syndrome (AIDS) occurs when the body loses the ability to fight infection. AIDS is caused by the human immunodeficiency virus (HIV). AIDS gradually destroys the body’s helper T cell population, leading to susceptibility to secondary infections.

AIDS (cont.)