Question

1. Describe at least 3 physical and 3 chemical factors in the first line of defense for innate immunity.

Answer 1

Innate immune system is the first line of host defense against microbial attack. Innate immunity functions since the time of birth. It is non specific with little memory, innate immune system gets immediately active after encountering a foreign body without any delay.

Physical barriers (Innate immune system)

1. Skin- It is the first line of barrier. It checks the entry of pathogens inside the body. The epithelial cells of skin are dead and compactly packed. This tight compaction prevents entry of any microbe inside the cell.

2, Mucus membranes. The whole body is not covered by skin. The orifices like mouth, anal apertures are protected by mucus secreting membranes. Mucus is viscous fluid which covers the microbes and stops there attachment and entry inside cells

3. Cilia- Cilia with it's undulating movement plays a significant role in detaching attached microbes from the respiratory tract and plats a significant role of first line of defense in innate immune response. Cilia and mucus along with coughing response throw away the stuck pathogen.

Apart from the above mentioned physical barriers there are others like directional flow of liquid (in intestine as well as during urination) expels and removes huge microbial load and forms an important component of first line of innate immune response.

Chemical barrier at surface (Innate immune system)

Low pH in some areas like in vaginal lining offers significant resistance to bacterial invasion.

1. Lysozyme- Is an important enzyme which acts as fist line chemical barrier under innate immune response. Lysozyme forms a major component of several bodily secretions like tears, sweat and respiratory fluids. Lysozyme breaks the peptidoglycan present in bacterial cell wall and thereby kill them by lysis.

2. Psoriasin- It is present in skin secretion and it is particularly effective against E.coli. Since E.coli is present in huge amount in our faecal matter. Controlling E coli population in our skin is of paramount importance. Psoriasin kills the E.coli within 30 minutes.

3. Other Small peptides - Several small polypeptides ( less than 100 amino acid in length) with antimicrobial capacity are also found

For example- alpha/beta defensins along with cathelicidins are secreted by several epithelial cells of different tissues. They have potent antimicrobial activity against P. aeroginosa and S. pneumoneae.

Apart from these, there are some chemicals which are secreted in milk, nasal fluids and tears like lactoferrin and calprotectin which chelate metal ions and have significant bacteriostatic effects. Lactoferrin also helps in hydrolyzing RNA. Therefore, it offers protection against several RNA viruses.