Innate Immunity

What is innate immunity?

also known as non-specific immune system, comprises the cells and mechanisms that defend the host from infection by other organisms in a non-specific manner (natural).

What are the two parts to innate immune system?

First line & second line

First line

1. Mechanical Barriers

2. Chemical & biochemical inhibitors

3. Normal flora

Second line

1. Cells - NK, Phagocytes

2. Soluble factors

3. Inflammatory barriers

Machanical barriers

1. Intact skin

2. Mucous coat

3. Mucous secretion

4. Blinking reflex and tears

5. The hair at the nares (nostrils)

6. Coughing and sneezing reflex

Chemical & biochemical inhibitors

1. Sweat and sebaceous secretion

2. Hydrolytic enzymes in saliva

3. HCl of the stomach

4. Proteolytic enzyme in small intestine

5. Lysozyme in tears

6. Acidic pH in the adult vagina

Normal bacterial flora

1. Competition for essential nutrients 2. Production of inhibitory substances

(to inhibit bacterial growth)

Natural Killer (NK) cells

Large granular lymphocytes, Innate cytotoxic (Toxic to Ag) lymphocytes, Source is bone marrow precursors, 10% or 15% of lymphocytes are located in peripheral blood, 1% or 2% of lymphocytes located in spleen, CYTOTOXIC FOR: tumor cells, viral infected cells, bacterial, fungal, parasitic infection. Responsible for antibody-dependent cell mediated cytotoxicity (ADCC)

Antibody-dependent cell mediated cytotoxicity (ADCC)

mechanism of cell-mediated immunity whereby an effector cell of the immune system actively lyses a target cell that has been bound by specific antibodies.

Phagocytes

are the white blood cells that protect the body by ingesting (phagocytosing) harmful foreign particles, bacteria, and dead or dying cells

Polymorphonuclear leukocytes

also called granulocytes but mainly refers to neutrophil granulocytes (most abundant granulocyte). They are released from the bone marrow by the regulatory complement proteins.

Mononuclear phagocyte system

is a part of the immune system that consists of the phagocytic cells located in reticular connective tissue(is a type of connective tissue. It has a network of reticular fibers, made of type III collagen). The cells are primarily monocytes and macrophages, and they accumulate in lymph nodes and the spleen. The Kupffer cells of the liver and tissue histiocytes are also part of the MPS.

NB*

"Reticuloendothelial system" is an older term for the mononuclear phagocyte system, but it is used less commonly now, as it is understood that most endothelial cells are not macrophages.

SOLUBLE FACTORS

1- Acute phase protein (Plasma protein, CRP=C reactive protein, Fibrin.)

2- Complement (proteins in serum, serosal, body fluids)

3- Interferons(Proteins against viral infections)

4- Properdin (Complement activation)

5- Beta lysine (Antibacterial protein from Platelets)

6- Lactoferrin,Transferrin (Iron binding protein)

7- Lactoperoxidase (Saliva & Milk)

8- Lysozyme (Hydrolyze cell wall)

Acute-phase proteins

are a class of proteins whose plasma concentrations increase (positive acute-phase proteins) or decrease (negative acute-phase proteins) in response to inflammation. This response is called the acute-phase reaction (also called acute-phase response). *C-reactive protein (CRP) is a protein found in the blood, the levels of which rise in response to inflammation (i.e. C-reactive protein is an acute-phase protein). Its physiological role is to bind to phosphocholine expressed on the surface of dead or dying cells (and some types of bacteria) in order to activate the complement system via the C1Q complex.

Complement

helps or "complements" the ability of antibodies and phagocytic cells to clear pathogens from an organism

Interferon

belong to the large class of glycoproteins known as cytokines. Interferons are named after their ability to "interfere" with viral replication within host cells.

Properdin (factor P)

is a globulin protein found in the blood serum of more complex animals. In the complement system, an innate-immunity series of proenzymes dissolved in the circulation, it is also called "Factor P".

Beta lysine

3,6-diaminohexanoic acid) is an amino acid produced by platelets during coagulation and is directly antibacterial by causing lysis of many Gram positive bacteria by acting as a cationic detergent.

Transferrins

are iron-binding blood plasma glycoproteins that control the level of free iron in biological fluids.

Lactoperoxidase

is a peroxidase enzyme secreted from mammary, salivary, and other mucosal glands that functions as a natural antibacterial agent.

Lysozyme

also known as muramidase or N-acetylmuramide glycanhydrolase, are glycoside hydrolases, enzymes that damage bacterial cell walls by catalyzing hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins. Lysozyme is abundant in a number of secretions, such as tears, saliva, human milk, and mucus. It is also present in cytoplasmic granules of the polymorphonuclear neutrophils (PMN).