The Immune System; Part I Medgar Evers College, CUNY Bio 261; Microbiology Dr. Santos

Immunology The study of the physiological mechanisms that humans and animals use to defend their bodies from invasion by microorganisms. The immune system The tissues, cells, and molecules involved in host defense mechanisms, primarily against infectious agents.

There are four types of infectious agents. Bacteria, viruses, fungi, and parasites such as worms and protozoa. Anything foreign that enters your body and activates your immune system is called an ANTIGEN. Two major kinds of defense have evolved that counter these threats Innate immunity and acquired immunity

Innate Immunity Innate immunity Is present before any exposure to pathogens and is effective from the time of birth Involves nonspecific responses to pathogens Figure 43.1 3m

Acquired immunity, also called adaptive immunity Develops only after exposure to inducing agents such as microbes, toxins, or other foreign substances Involves a very specific response to pathogens

Innate Immunity 7 components 1- First line of defenses such as physical barriers, antimicrobial substances and the normal microbiota. 2- Specialized cells and chemicals they use to communicate with each other and the immediate environment.

3-Pattern recognition receptors to detect PAMP (pathogenic associated molecular patterns). 4- The Complement system 5- Phagocytosis 6- Inflammation 7- Fever

1-Physical barriers/chemicals Include the skin the mucous membranes Lysozyme, found in tears and mucus that bathe mucous membranes, destroys bacteria. Sweat is high in salt and when it evaporates leaves behind salt residues that inhibit bacterial growth.

Lactoferrins and tranferrins are iron binding proteins found in saliva, mucus and tears, blood and tissue fluids. They bind to Iron and doesn’t make it available for microbes. Microbes need Iron for growth. Defensins are produced by neutrophils and epithelial cells. They are short peptides that insert into the bacterial membrane forming pores and disrupting the integrity of the cell.

Normal microbiota The normal microbiota or flora is the population of bacteria living in your body.

2- cells and chemicals of communication

Granulocytes All granulocytes contain cytoplasmic granules with biologically active chemicals. 3 types of granulocytes are Neutrophils Basophils Eosinophils.

Neutrophils Are phagocytic cells that eat and destroys foreign material. They are specially effective against bacteria and damaged cells. Neutrophils are highly active, short lived (1 to 2 days) phagocytic cells that must be recruited to the site of damage.

Basophils Involved in allergic reactions and inflammation. The granules contain histamines and other chemicals that increase capillary permeability during inflammation. Mast cells are similar to them but only found in tissues.

Eosinophils The granules of eosinophils stain red with the acidic dye eosin. These blood cells are mainly involved in expelling parasitic worms from the body.

Mononuclear phagocytes (macrophages) They differentiate from a monocyte. Are present in virtually all tissues to at least some extend. Are phagocytic cells. Can live for weeks to a few months.

Dendritic cell Main scouts of the immune system. These cells are known as antigen presenting cells. They survey body fluids and tissues for potential pathogens and present the antigen to T cells.

Cell communication Cells of the Immune system must communicate with each other and their immediate environment in order to effectively do their job. They do this through surface receptors, cytokines, and adhesion molecules.

List of cytokines These are proteins secreted by blood cells to communicate with other cells. They bind to cytokine receptors that are found on cells they regulate.

Types of cytokines include; 1-Chemokines. 2- Colony stimulating factors 3- Interferons, INF, are important against viral infections. 4- Interleukins 5- Tumor necrosis

3- Pattern recognition receptors These pattern recognition sensor systems allow the body to detect foreign material. They include the Toll like receptors and NOD proteins.

Toll like receptors are types of proteins that specifically look out for foreign microbes and help activate the Immune response. Both These receptors specifically look out for peptidoglycan, flagellin, LPS, bacterial plasmids, bacterial DNA or anything that signals a foreign invasion.

4- The complement system The complement system is a series of proteins that circulate in the blood and the fluids that bathe the tissues and organs. 3 ways to activate Classical (antibody-antigen) Alternative (C3b binding to invader) Lectin (Mannose binding lectin binding to invader)

5- Phagocytosis Phagocytes attach to their prey via surface receptors And engulf them, forming a vacuole that fuses with a lysosome Microbes MACROPHAGE Vacuole Lysosome containing enzymes Pseudopodia surround microbes. 1 Microbes are engulfed into cell. 2 Vacuole containing microbes forms. 3 Vacuole and lysosome fuse. 4 Toxic compounds and lysosomal enzymes destroy microbes. 5 Microbial debris is released by exocytosis. 6 Figure 43.4

6- Inflammatory Response In local inflammation, histamine and other chemicals released from injured cells Promote changes in blood vessels that allow more fluid, more phagocytes, and antimicrobial proteins to enter the tissues. The vital role of inflammation is to contain the infection, localize the response, and restore proper tissue function. Four cardinal signs are swelling, redness, heat, pain, and a fifth is loss of function.

7- fever Is a strong indicator of an infectious disease. They elevate body temperature and make the internal conditions more hostile to the pathogens.