How does our body protect us from pathogens?

I am going to ask a few question:

How aften do you sanitize your phone, earphones, chargers etc?....do you think its clean or sterile.

Forget about your phone, how often do you wash/ sanitize your Hands? May be one or two times a day (Its due to COVID era). Do you think its enough?

There are some theory suggest, your mobile can be 10 times more dirtier then toilet seats.

Your Bathroom towel,Handbags,Remote control,keyboards,Fridge etc...daily items contain more pathogens then you can imagine.

And there are some Bacteria like Streptococcus, which can survive in this items ,upto 6 months.Many Fungi, Viruses, Bacteria can stick to this objects for a considerable amount of time and can cause various infection. And if you know or have any elderly or Immunocompromised people in your home, then there is more risk of infection for them.

But do you think how often you got infection ? (Except elderly or Immunocompromised people)

Maybe 1- 2 times a month and,if you are healthy then, you may not remember when you had infection.

Thanks to our Immune system, because it protect us from all these harmful pathogen.

Now i am going to explain how it protects:

Basically Our immune system is divided int two types i.e.

Native/Naive/Natural/Innate Immunity
Acquired/Adaptive immunity

Lets start the explanation:

1. Native/Naive/Natural/Innate Immunity

As the name suggest , its the natural defence mechanism that provide immediate but non specefic protection against pathogens. As a result it doesnot confer long-lasting Immunity. But it can activates Adaptive immunity via various processes ,which provides targeted, long-term protection against specific pathogens. But its the first line of defence against pathogens and is always ready to respond to invading microorganisms.

1.Physical Barriers:

Our very known, skin and mucous membranes act as physical barriers that prevent pathogens from entering the body. The skin forms a tough barrier that is difficult for pathogens to penetrate, while mucous membranes line the respiratory, gastrointestinal, and genitourinary tracts, producing mucus that traps and removes pathogens.

2.Chemical Barriers:

Various chemicals which are relased in our body, such as enzymes, antimicrobial peptides, and low pH environments (in stomach), help to destroy or inhibit the growth of pathogens. For example, stomach acid kills many ingested pathogens, while enzymes in tears and saliva break down bacterial cell walls.

3.Cellular Components:

Innate immunity involves specialized cells that recognize and eliminate pathogens. Some Phagocytes like neutrophils and macrophages, engulf and digest foreign particles. Also Natural killer (NK) cells detect and destroy infected or cancerous cells.

4.Inflammatory Response:

When tissues are damaged or infected, the body initiates an inflammatory response. This involves the release of chemical mediators, such as histamine and cytokines, which increase blood flow to the affected area and attract immune cells to eliminate pathogens and promote tissue repair.

These are the first line of defence but now comes the main heroes, who can kill and remember its enemy and protect us from subsequent infection.

2.Acquired or Adaptive Immunity

Unlike innate immunity, which provides immediate, nonspecific defense, acquired immunity is highly specific to particular pathogens and involves a memory component that enables a faster and stronger response upon subsequent exposure.

Acquired immunity relies on the recognition of specific antigens, which are molecules on the surface of pathogens or other foreign substances.

This immunity involves Lymphocytes i.e B cells and Tcells.

B cells are white blood cells which is present in our blood that produce antibodies that bind to antigens and cause destruction of the pathogens.

While T cells, which are also present in our blood, directly attack infected cells or regulate immune responses.

One of the intresting features of acquired immunity is its ability to "remember" previous encounters with pathogens. After initial exposure, B cells and T cells undergo clonal expansion and differentiation into memory cells, which persist in the body for long periods. Upon re-exposure to the same antigen, memory cells mount a rapid and robust immune response, leading to faster clearance of the pathogen and often providing long-lasting protection against reinfection.

Acquired immunity can be divided into two main types:

Humoral immunity
Cell-mediated immunity.

Humoral immunity involves the production of antibodies (immunoglobulins, Y shaped protein)by B cells, which circulate in the bloodstream and target pathogens or toxins in body fluids.

Cell-mediated immunity which is mainly mediated by T cells. It targets infected or abnormal cells directly and is particularly important for combating intracellular pathogens, such as viruses.

These cells are located throughout our body, i.e Tonsil which contains cluster of lymphoid tissue, Spleen which contain B cells, T cells, Macrophages etc.

Its also located in Mucosal surfaces like:

GALT(Gut-Associated Lymphoid Tissue) which includes structures like Peyer's patches and lymphoid follicles located in the intestines. They contain immune cells, such as B cells, T cells, and dendritic cells, that monitor the gut for pathogen.

Mucosa-Associated Lymphoid Tissue (MALT) which includes lymphoid tissues found in mucosal surfaces throughout the body, such as the respiratory tract (bronchus-associated lymphoid tissue, BALT) and the genitourinary tract. These tissues contain immune cells that defend against pathogens entering through mucosal membranes.

And also in our general tissues like:

Skin: Langerhans cells, dendritic cells, and resident T cells populate the skin, providing local immune surveillance and defense against skin pathogens.

Respiratory Tract: Immune cells, including macrophages, dendritic cells, and lymphocytes, are present in the respiratory tract, guarding against inhaled pathogens and maintaining lung health.

Central Nervous System (CNS): Microglia, a type of immune cell, reside in the CNS and play a role in immune surveillance and response within the brain and spinal cord.