In the fascinating world of immunology, our body possesses a remarkable defense system known as the immune system. It is responsible for protecting us from harmful pathogens and foreign invaders. The immune system consists of two major components: innate immunity and adaptive immunity. While adaptive immunity provides a specific and long-lasting defense, innate immunity serves as the first line of defense against various pathogens. In this article, we will explore the biochemical factors that contribute to innate immunity and their significance in keeping us healthy.
Introduction
Innate immunity is the first line of defense that our body utilizes to protect against infectious agents. It is a rapid response system that does not require prior exposure to a specific pathogen. Innate immunity is present from birth and provides immediate protection, acting as a barrier to prevent the entry and spread of pathogens.
The following biochemical factors are employed to fight against infectious organisms:
1. Secretions of the skin
2. Secretions of the digestive tract
3. Human milk
4. Nasal secretion and saliva
5. Lysozyme
6. Interferons
7. Complement
8. Properdin
9. Secretions of bacterial flora
10. Semen
11. Acute phase proteins.
Secretions of the Skin
- The high concentration of salt in the sweat possesses bactericidal activity.
- The acidity of sweat and thereby low pH (pH 5.5) has microbicidal effect.
- The secretions of the sebaceous and sweat glands act as antiseptics as they contain lactic acid and fatty acids which have bactericidal and fungicidal properties.
- But certain areas of the body, namely, soles of the feet are deficient of sebaceous glands and thereby these areas are more attacked by fungal growth and hence such areas are sometimes referred as ‘alkaline gaps’.
Secretions of the Digestive Tract
- The high acidity of the stomach (pH 2.0) has a microbicidal effect and this is due to the presence of HCI in the gastric juice which is secreted by the oxynctic cells lining the stomach.
Human Milk
- Human milk is rich in antibacterial substances, namely lactoferritin and neuraminic acid.
- They fight against E.coli and Staphylococci.
- Nasal Secretion and Saliva
- These secretions contain mucopolysaccharides which inactivate certain viruses.
Lysozyme
- Tears, nasal secretions, saliva, polymorphonuclear leukocytes, human milk and most tissue fluids (except cerebro spinal fluid -CSF, sweat and urine) contain a mucolytic enzyme N-acetyl-muramidase, known as lysozyme.
- This was first discovered by Fleming in 1992 and it is a low molecular weight basic protein which helps in the lysis of many Gram-positive bacteria by splitting of the sugars from the glycopeptides of the cell wall.
- In the presence of additional serum complement factors, it can digest some of the Gram-negative bacteria also. Egg white is a rich commercial source of lysozyme.
Interferons (IFN)
- Interferons are a group of soluble, non-toxic, glycoproteins produced in small amounts by all the cells of the body.
- This is an antiviral agent which inhibits intracellular viral replication in cells infected with viruses.
- Interferon appears in the cells before any detectable antibody for the viruses could appear. It offers resistance by blocking viral mRNA transcription thereby disrupting the viral life cycle.
- Interferons also enhance NK cell activity, thus offering immunity to cancer. They also inhibit cell proliferation in tumours and thereby assuring its use in cancer chemotherapy.
- Because of their antiviral and anticancer properties, large quantities of interferon is commercially prepared to help in the treatment of viral infection and in cancer therapy.
- The manufacture of interferons is a major breakthrough in Science, as genes for human interferons have been introduced in E.coli genome to produce interferons by E.coli. (DNA Recombinant Technology).
- On the basis of their electrophoretic mobility, the interferons are grouped into α- interferon (IFN α), β -interferon (IFN β) and ϒ-interferon (IFN ϒ). ϒ-interferon is specifically produced only by activated T lymphocytes.
Complement
- The complement is a complex system of enzymatic proteins found in the serum and is activated by antigen-antibody complexes.
- Activation of the complement increases phagocytosis and destruction of the microbial organisms that enter an individual.
- Complement operates by three major mechanisms, namely the classical, alternative and the lectin pathways.
- The main function of complement is the opsonization of microorganisms and the formation of membrane attack complex (MAC) there by promoting their phagocytosis and lysis.
Properdin
- This is a group of proteins present in the normal serum and is involved in resistance to infections.
- Along with complement and Mg”, this causes lysis of Gram-negative bacteria and also inactivates certain viruses.
Secretions of Bacterial Flora
- The bacterial flora of the skin produces various antimicrobial substances such as bacteriocins and acids.
- The bacterial flora of the human gut live as commensals. They secrete colicin and acids which do not allow the entry of other microorganisms into the body. They also stimulate the immune system to function against other microbial antigens. If the commensals of the gut are removed by antibiotics, the pathogenic organisms gain easy entry.
- The Lactobacilli in vagina produce antibacterial acid. Moreover the microflora of the mucous membrane prevent proliferation of pathogenic organisms by producing inhibitory substances like hydrogen peroxide, antibiotics or by altering the pH to make it unsuitable for the growth of other microbes.
Semen
- It contains bactericidal components, namely spermine and zinc.
Acute Phase Protein
- This is a group of plasma proteins which increase very rapidly during infection. One example of this group is C-reactive protein (CRP), which is called so because of its ability to bind the C-protein of Pneumococci. The CRP acts as opsonins and the bacteria bound CRP protein activates the complement which facilitates its uptake by phagocytosis.