An especially elaborate and important type of innate antimicrobial enzymes defense is provided by a group of serum proteins that together make up the complement cascade pathway. This group comprises more than two dozen different liver-and macrophage-derived proteins, called complement factors or components, most of which normally circulate in the form of proenzymes that have latent protease activity. As a rule, each of the proteases becomes active when proteolytically cleaved and will then catalyze cleavage and activation of a different complement component. (more…)

A few of the best known humoral effectors of innate immunity are listed in Table 1 bellow, along with the types of target molecules they recognize. Some are enzymes that can directly injure or kill microbial pathogens. An example is lysozyme, an endoglycosidase found in human saliva, mucus, tears, and other secretions, which attacks the protective cell wall encasing every bacterial cell. Lysozyme acts by digesting the peptidoglycan meshwork formed by long carbohydrate chains of alternating N-acetylmuramic acid and N-acetylglucosamine residues, crosslinked covalently by short oligopeptide sidechains which is a major constituent of all bacterial cell walls but is not found in mammalian tissues. (more…)

Routes by which infectious organisms gain entry into the body include the skin, respiratory tract, gastro-intestinal (GI) tract and GU tract. There are fundamentally two ways in which infectious agents cross the physical and chemical barriers: either they are able to penetrate the intact barriers at one or more anatomical sites, or the physical barriers are damaged and breached, allowing entry of the organism.

Bellow are some possibles pathogens entry into human body:

Penetration of intact skin or mucosa

• Skin. Few organisms are able to penetrate intact skin. However, some parasites (e.g. hookworm) or their larvae (e.g. schistosoma) can do this. Other agents, such as wart viruses, set up infection in the skin and do not enter further into the body.

• Mucosa. Mucosa, being softer and damper than skin, are much more frequent sites of entry and all intact mucosa can be penetrated by some organisms. Examples are shown in table bellow. Pathogens can cross epithelia by passing through epithelial cells, as in the case of the meningococcus (a bacteria causing meningitis), or by passing between the epithelial cells, seen with Haemophilus influenzae.

Mucosal Sites of Entry for Pathogens

Penetration of damaged skin or mucosa

There are many ways in which skin or mucosa can be damaged, allowing entry of infectious organisms that could not cross intact skin or mucosa. Damage to skin is a particularly important route of infection and can occur in a number of ways:

• Burns. Burns, especially severe ones, pose a major risk for infection, particularly with Staphylococcus, Streptococcus, Pseudomonas and Clostridium tetanus.

• Cuts and wounds. These can allow entry of similar organisms to those seen after burns.

• Insect bites. Numerous infections pathogenesis are transmitted via insect bites. These include malaria, typhus and plague.

• Animal bites. Animal bites can provide direct transmission of infection, such as in rabies. Because they cause significant damage to the skin, bites can allow the entry of the same environmental pathogens as burns, cuts and wounds (see above).

• Human behaviour. Various aspects of uniquely human behaviour can result in the skin being penetrated. Sharing of syringes by intravenous (IV) drug users exposes them to risk of hepatitis and human immunodeficiency virus (HIV). A number of viral infections (hepatitis, HIV) have been transmitted by blood transfusion and blood products (e.g. factor VIII for haemophiliacs) before appropriate screening procedures were developed. Transplantation has also resulted in transmission of infection before the introduction of appropriate donor screening.

Damage to mucosa may not increase the likelihood of infection to the same extent as damage to the skin. However, physical or chemical damage may allow entry of some organisms (e.g. smoking increases the risk of respiratory bacterial infections or respiratory allergies). Furthermore, infection of the mucosa with a virus may cause damage and facilitate the entry of bacterial pathogens spread.

There are several pathogen types that can cause disease include many groups of single-celled microorganisms and larger multicellular parasites. Viruses, bacteria, some yeasts, and protozoan parasites are examples of single- celled pathogens. Fungi and helminths (parasitic worms) are the major multi-cellular pathogens. These pathogens come from very different parts of the biological kingdom and vary considerably in many aspects. Pathogens differ enormously in their size. They also have very different lifestyles and cause disease in a variety of ways like bellow:

Poliovirus (Viruses)

Size: 20–400nm
Habitat: Intracellular: pharynx, intestine, nervous system
Mode of multiplication: Intracellular synthesis of viral components
Multiplication rate (doubling time): <1 hour

Poxvirus (Viruses)

Size: 20–400nm
Habitat: Intracellular: upper respiratory tract, lymph nodes, skin
Mode of multiplication: Intracellular synthesis of viral components
Multiplication rate (doubling time): <1 hour

Streptococcus pyogenes (Bacteria)

Size: 1–5µm
Habitat: Extracellular: pharynx
Mode of multiplication: Cell fission
Multiplication rate (doubling time): 3 hours

Mycobacterium leprae (Bacteria)

Size: 1–5µm
Habitat: Intracellular: macrophages, endothelial cells, Schwann cells
Mode of multiplication: Cell fission
Multiplication rate (doubling time): 2 weeks

Candida albicans (Fungi)

Size: 2–20µm
Habitat: Extracellular: mucosal surfaces
Mode of multiplication: Asexual budding
Multiplication rate (doubling time): Hours

Histoplasma capsulatum (Fungi)

Size: 2–20µm
Habitat: Intracellular: macrophages
Mode of multiplication: Asexual budding
Multiplication rate (doubling time): Hours

Trypanosomes (Protozoan parasites)

Size: 1–50mm
Habitat: Extracellular: bloodstream
Mode of multiplication: Binary fission
Multiplication rate (doubling time): 6.5 hours

Plasmodium (Protozoan parasites)

Size: 1–50mm
Habitat: Intracellular: red blood cells, hepatocytes
Mode of multiplication: Asexually in hepatocytes (cell fission)
Multiplication rate (doubling time): 8 hours

Ascaris lumbricoides (Metazoan parasites worms)

Size: 3mm to 7m
Habitat: Intestine
Mode of multiplication: Lays eggs
Multiplication rate (doubling time): 200000 eggs/day

Taenia solium tapeworm (Metazoan parasites worms)

Size: 3mm to 7m
Habitat: Gut
Mode of multiplication: Releases body segments containing eggs
Multiplication rate (doubling time): 800000 eggs/day

Size of pathogens

One feature of the range of pathogenic organisms listed above is the enormous variation in size. Viruses are the smallest infectious organisms, being 20–400 nm in size. At the other end of the scale some parasitic worms, such as the tapeworm, can be up to 7 m (20 ft) in length. This represents a difference in scale of a factor of 10e9 . To put that into some sort of perspective, if a virus were the size of a tennis ball, a fully developed tape- worm would reach from London to Los Angeles. It does not stretch the imagination too far to appreciate that the problems posed to the immune system by these two organisms would require very different solutions.

Stages of disease production by pathogens

Size is not the only way in which infectious organisms vary. They also vary enormously with respect to how they enter and live within the body and actually cause disease. Infection and disease production by pathogenic organisms can be divided into four stages:

1. Invasion.
2. Multiplication.
3. Spread.
4. Production of disease (pathogenesis).

Although infection usually involves all of these steps, there are many exceptions in terms of both the steps involved and their order. Some pathogens do not spread significantly or even technically gain entry to the body. Organisms may replicate locally before spreading or may spread through the body before beginning significant replication. Pathogens show considerable variation at each of these stages of infection, as will be described below.

The way in which pathogens spread through the body is influenced to some extent by whether they live intra-cellularly, extra-cellularly or both. Organisms that live extra-cellularly are able to spread via body fluids such as blood. However, even organisms that replicate intra-cellularly may be able to leave the cell and spread via an extracellular route. Organisms can spread in the following ways: (more…)

There are thousands of components to the immune system, and during the course of learning about some of these it can appear that the immune system is far more complex and complicated than necessary for achieving what is, on the surface, the simple task of eliminating an infectious organism. There are a number of reasons why the immune system is complex. The first of these is the desirability of eliminating pathogens without causing damage to the host. Getting rid of a pathogen is theoretically easy. If you had an infection in your liver you could produce a nasty toxin that would kill the pathogen; unfortunately it would also destroy your liver. Killing pathogens is not difficult, but getting rid of pathogens without damaging the host is much more complicated. (more…)

Natural killer cells: history and current status

Natural killer cells are a major component of the immune system, which play important roles in host defense against cancer and microbial infections. Natural killer cells are distinct from T or B lymphocytes, with a characteristic morphology of large granular cells, and can be readily identified by characteristic cell surface molecules. (more…)

It is estimated that more than 12 millions of American are having food allergy. About 4 percent of adults are having this disease and nearly 6 to 9 percent children under the age of 3 are having the same illness. The prevalence of food allergies is rising, where the most common food allergy in children are caused by milk allergy in children, eggs, peanuts allergy and tree nuts. In adults, the most common allergic reaction are triggered by peanuts, tree nuts, shellfish, fish and eggs. (more…)

Immune system is your body’s defense mechanism to protect from infectious organism and other living object invaded your body. The body reacts through several cellular immune response, and immune system attacks those foreign objects which may cause disease. Immune system consisted of network cells, skins, tissue and organs which work closely to protect body. How immune system works?

Immune system is so important for us to survive since we are surrounded by virus, fungus, parasite and bacteria which always trying to break into our body. (more…)