INNATE (NON-SPECIFIC) IMMUNITY

The elements of the innate (non-specific) immune system include anatomical barriers, secretory molecules and cellular components. 

Among the mechanical anatomical barriers are the skin and internal epithelial layers, the movement of the intestines and the oscillation of broncho-pulmonary cilia. 

Associated with these protective surfaces are chemical and biological agents.

A. Anatomical barriers to infections

1. Mechanical factors

The epithelial surfaces form a physical barrier that is very impermeable to most infectious agents. Thus, the skin acts as our first line of defense against invading organisms. The desquamation of skin epithelium also helps remove bacteria and other infectious agents that have adhered to the epithelial surfaces. 

2. Chemical factors

Fatty acids in sweat inhibit the growth of bacteria. Lysozyme and phospholipase found in tears, saliva and nasal secretions can breakdown the cell wall of bacteria and destabilize bacterial membranes. The low pH of sweat and gastric secretions prevents growth of bacteria. Defensins (low molecular weight proteins) found in the lung and gastrointestinal tract have antimicrobial activity. Surfactants in the lung act as opsonins (substances that promote phagocytosis of particles by phagocytic cells). 

3. Biological factors

The normal flora of the skin and in the gastrointestinal tract can prevent the colonization of pathogenic bacteria by secreting toxic substances or by competing with pathogenic bacteria for nutrients or attachment to cell surfaces.

B. Humoral barriers to infection

Humoral factors play an important role in inflammation, which is characterized by edema and the recruitment of phagocytic cells. These humoral factors are found in serum or they are formed at the site of infection.

1. Complement system – The complement system is the major humoral non-specific defense mechanism (see complement chapter). Once activated complement can lead to increased vascular permeability, recruitment of phagocytic cells, and lysis and opsonization of bacteria. 

2. Coagulation system – Depending on the severity of the tissue injury, the coagulation system may or may not be activated. Some products of the coagulation system can contribute to the non-specific defenses because of their ability to increase vascular permeability and act as chemotactic agents for phagocytic cells. In addition, some of the products of the coagulation system are directly antimicrobial. For example, beta-lysin, a protein produced by platelets during coagulation can lyse many Gram positive bacteria by acting as a cationic detergent.

3. Lactoferrin and transferrin – By binding iron, an essential nutrient for bacteria, these proteins limit bacterial growth.

4. Interferons – Interferons are proteins that can limit virus replication in cells.

5. Lysozyme – Lysozyme breaks down the cell wall of bacteria. 

6. Interleukin -1 – Il-1 induces fever and the production of acute phase proteins, some of which are antimicrobial because they can opsonize bacteria.

C. Cellular barriers to infection

Part of the inflammatory response is the recruitment of polymorphonuclear eosinophiles and macrophages to sites of infection. These cells are the main line of defense in the non-specific immune system.

1. Neutrophils – Polymorphonuclear cells  are recruited to the site of infection where they phagocytose invading organisms and kill them intracellularly. In addition, PMNs contribute to collateral tissue damage that occurs during inflammation.

2. Macrophages – Tissue macrophages  and newly recruited monocytes , which differentiate into macrophages, also function in phagocytosis and intracellular killing of microorganisms. In addition, macrophages are capable of extracellular killing of infected or altered self target cells. Furthermore, macrophages contribute to tissue repair and act as antigen-presenting cells, which are required for the induction of specific immune responses.

3. Natural killer (NK) and lymphokine activated killer (LAK) cells – NK and LAK cells can nonspecifically kill virus infected and tumor cells. These cells are not part of the inflammatory response but they are important in nonspecific immunity to viral infections and tumor surveillance. 

4. Eosinophils – Eosinophils  have proteins in granules that are effective in killing certain parasites.

Method of Sterilization for common items

Autoclaving :  Animal cages, Sugar tubes, Lab. Coats, Cotton , Filters, Instruments Culture media, Rubber, Gloves , Stopper, Tubing, Slides,  Syringe and Wax needles , Test tubes, Enamel metal trays ,Wire baskets, Wood, Tongue depressor, Applicator, Endodontic instruments, Orthodontic pliers , Orthodontic kits, Saliva ejector, Handpieces Cavitron heads, Steel burs, Steel tumbler, Hand instruments    

Hot air oven

Beakers, Flasks, Petri dish, Slides, Syringes, Test tubes, Glycerine, Needles ,Oil, Paper Saliva ejector, Matrix Band

Ethylene oxide

Fabric, Bedding, Blanket, Clothing, Matteresses, Pillows, Disposable instruments , Instruments, Blades, Knives, Scalpels, Scissors ,Talcum powder, Books, Cups, plates , Plastics., Flask, Petridish, Tubes, Tubing, Rubber , catheters, Drains, Gloves ,Special items - Bronchoscope, Cystoscope, Heart lung machine

Glutaraldehyde

Orthodontic kits, Orthodontic pliers , Steel burrs, 3 in 1 syringe tips ,Cystoscope ,Endoscope

Filtration

Antibiotics, Serum, Vaccines
 

Autoantibodies

Anti-nuclear antibodies (ANA)    Systemic Lupus
Anti-dsDNA, anti-Smith               Specific for Systemic Lupus
Anti-histone                                 Drug-induced Lupus
Anti-IgG                                       Rheumatoid arthritis
Anti-neutrophil                             Vasculitis
Anti-centromere                           Scleroderma (CREST)
Anti-Scl-70                                   Sclerderma (diffuse)
Anti-mitochondria                         1^oary biliary cirrhosis
Anti-gliadin                                   Celiac disease
Anti-basement membrane            Goodpasture’s syndrome
Anti-epithelial cell                          Pemphigus vulgaris
Anti-microsomal                            Hashimoto’s thryoiditis

Measurement of Bacterial of Growth

A convenient method is to determine turbidity by photoelectric colorimeter or spectrophotometer. 
The cell number can be counted as total cell number as well as viable count. Viable Count Viable number of bacteria can be counted by inoculating the suspension onto solid growth medium and counting the number of colonies. Since each colony is the end product of one viable bacterium, their count gives the number of viable bacteria in the suspension.
Total number of bacteria can be ascertained in specially designed chambers such as Coulter counter.
 

CELLS ORGANELLES

Cell parts:

Mitochondrion – double MB structure responsible for cellular metabolism – powerhouse of the cell

Nucleus – controls synthetic activities and stores genetic information

Ribosome – site of mRNA attachment and amino acid assembly, protein synthesis

Endoplasmic reticulum – functions in intracellular transportation

Gogli apparatus/complex – composed of membranous sacs – involved in production of large CHO molecules & lysosomes

Lysosome – organelle contains hydrolytic enzymes necessary for intracellular digestion

Membrane bag containing digestive enzymes

Cellular food digestion – lysosome MB fuses w/ MB of food vacuole & squirts the enzymes inside. Digested food diffuses through the vacuole MB to enter the cell to be used for energy or growth. Lysosome MB keeps the cell iself from being digested 

-Involved mostly in cells that like to phagocytose
-Involved in autolytic and digestive processes
-Formed when the Golgi complex packages up an especially large vesicle of digestive enzyme proteins

Phagosome 
– vesicle that forms around a particle (bacterial or other) w/in the phagocyte that engulfed it
- Then separates from the cell membrane bag & fuses w/ lysozome to receive contents
- This coupling forms phagolysosomes in which digestion of the engulfed particle occurs

Microbodies:
- Contain catalase
- Bounded by a single membrane bag
-  Compartments specialized for specific metabolic pathways
-  Similar in function to lysosomes, but are smaller & isolate metabolic reactions involving H2O2

-  Two general families:
·        Peroxisomes: transfer H2 to O2, producing H2O2 – generally not found in plants
·        Glyoxysomes: common in fat-storing tissues of the germinating seeds of plants
¨      Contain enzymes that convert fats to sugar to make the energy stored in the oils of the seed available

 Inclusions

– transitory, non-living metabolic byproducts found in the cytoplasm of the cell
- May appear as fat droplets, CHO accumulations, or engulfed foreign matter.

STRUCTURE AND SOME PROPERTIES OF IG CLASSES AND SUBCLASSES

A.  IgG

1. Structure

 All IgG’s are monomers (7S immunoglobulin). The subclasses differ in the number of disulfide bonds and length of the hinge region.

2. Properties

IgG is the most versatile immunoglobulin because it is capable of carrying out all of the functions of immunoglobulin molecules.

a) IgG is the major Ig in serum – 75% of serum Ig is IgG

b) IgG is the major Ig in extra vascular spaces

c) Placental transfer – IgG is the only class of Ig that crosses the placenta. Transfer is mediated by a receptor on placental cells for the Fc region of IgG. Not all subclasses cross equally well; IgG2 does not cross well.

d) Fixes complement – Not all subclasses fix equally well; IgG4 does not fix complement

e) Binding to cells – Macrophages, monocytes and neutrophils and some lymphocytes have Fc receptors for the Fc region of IgG.  A consequence of binding to the Fc receptors on such cells  is that the cells can now internalize the antigen better. The antibody prepares the antigen for killing by the phagocytic cells. The term opsonin is used to describe substances that enhance phagocytosis. (Coating of the surface of pathogen by antibody is called opsonization).IgG is a good opsonin. Binding of IgG to Fc receptors on other types of cells results in the activation of other functions.

IgM

1. Structure
 IgM normally exists as a pentamer (19S immunoglobulin) but it can also exist as a monomer. In the pentameric form all heavy chains are identical and all light chains are identical. Thus, the valence is theoretically 10. IgM has an extra domain on the mu chain (CH4) and it has another protein covalently bound via a S-S bond called the J chain. This chain functions in polymerization of the molecule into a pentamer.

2. Properties

a) IgM is the third most common serum Ig.

b) IgM is the first Ig to be made by the fetus and the first Ig to be made by a virgin B cells when it is stimulated by antigen.

c) As a consequence of its pentameric structure, IgM is a good complement fixing Ig. Thus, IgM antibodies are very efficient in leading to the lysis of microorganisms.

d) As a consequence of its structure, IgM is also a good agglutinating Ig . Thus, IgM antibodies are very good in clumping microorganisms for eventual elimination from the body.

e) IgM binds to some cells via Fc receptors.

f) B cell surface Ig 

Surface IgM exists as a monomer and lacks J chain but it has an extra 20 amino acids at the C-terminus to anchor it into the membrane . Cell surface IgM functions as a receptor for antigen on B cells.

IgA

1. Structure

Serum IgA is a monomer but IgA found in secretions is a dimer as presented in Figure 10. When IgA exits as a dimer, a J chain is associated with it.

When IgA is found in secretions is also has another protein associated with it called the secretory piece or T piece; sIgA is sometimes referred to as 11S immunoglobulin. Unlike the remainder of the IgA which is made in the plasma cell, the secretory piece is made in epithelial cells and is added to the IgA as it passes into the secretions . The secretory piece helps IgA to be transported across mucosa and also protects it from degradation in the secretions.

2. Properties

a) IgA is the 2nd most common serum Ig.

b) IgA is the major class of Ig in secretions – tears, saliva, colostrum, mucus. Since it is found in secretions secretory IgA is important in local (mucosal) immunity.

c) Normally IgA does not fix complement, unless aggregated.

d) IgA can binding to some cells – PMN’s and some lymphocytes.

IgD

1. Structure

 IgD exists only as a monomer.

2. Properties

a) IgD is found in low levels in serum; its role in serum  is uncertain.

b) IgD is primarily found on B cell surfaces where it functions as a receptor for antigen.

c) IgD does not bind complement.

E. IgE

1. Structure

IgE exists as a monomer and has an extra domain in the constant region.

2. Properties

a) IgE is the least common serum Ig since it binds very tightly to Fc receptors on basophils and mast cells even before interacting with antigen.

b) Involved in allergic reactions – As a consequence of its binding to basophils and mast cells, IgE is involved in allergic reactions. Binding of the allergen to the IgE on the cells results in the release of various pharmacological mediators that result in allergic symptoms.

c) IgE also plays a role in parasitic helminth diseases. Since serum IgE levels rise in parasitic diseases, measuring IgE levels is helpful in diagnosing parasitic infections. Eosinophils have Fc receptors for IgE and binding of eosinophils to IgE-coated helminths results in killing of the parasite.

d) IgE does not fix complement.