Our Wonderful Immunological System

 

In my last article I wrote about

“The Healing Properties of Our Body. Is Prevention Better than Cure?”

here:

https://scientificlogic.blogspot.com/2024/05/the-healing-properties-of-our-body-is.html

I mentioned about injuries such as bleeding, wounds, and fractures. It is not always we are injured and traumatised. But what we are facing every second, every minute in our lives are pathogenic organisms from the environment. These are far more threatening to our existence than occasional injuries such as cuts, bruises, and fractures from accidents. I thought it is only fair I should give priority to discuss a little bit how our body defend itself against invading pathogenic organisms from outside and within our bodies.  This is “Our Wonderful Immune System”. Later, perhaps I may deal with an internal threat from our own cells - cancer. But let me deal with infection first.  

The human body has a highly sophisticated and multi-layered defence system to protect itself against infections caused by pathogens such as bacteria, viruses, fungi, and parasites. This defence system can be broadly categorized into innate (nonspecific) and adaptive (specific) immunity. We shall briefly outline how each component works:

First, we have this innate immunity which can be classified as physical and chemical barriers. The skin for instance acts as a physical barrier preventing the entry of pathogens. It also produces antimicrobial proteins and peptides. Mucous membranes line the respiratory, gastrointestinal, and genitourinary tracts, trapping pathogens in mucus.

Secretions such as saliva, tears, and mucus contain enzymes like lysozyme that break down bacterial cell walls. Then there is this stomach acid where the acidic environment (low pH) destroys many ingested pathogens. Cilia which are tiny hair-like structures in the respiratory tract that move mucus and trapped pathogens out of the lungs.

Secondly, the body is also equipped with cellular defences that are the phagocytes, the white blood cells such as neutrophils and macrophages that engulf and digest pathogens. These phagocytes are made up of neutrophils which are the most abundant white blood cells that respond quickly to infections, the macrophages found in tissues and organs. They ingest pathogens and dead or dying cells.

Comes next the natural killer (NK) cells that destroy infected or cancerous cells by releasing cytotoxic granules that induce apoptosis (cell death). The blood also has the dendritic cells. These cells act as antigen-presenting cells that capture antigens and present them to T cells, initiating the adaptive immune response.

That’s not all. We have the inflammatory response that initiates inflammation, a process that isolates and limits tissue damage and infection. It involves vasodilation, an increased blood flow to the affected area, causing redness and heat. Increased permeability in the area allows immune cells and proteins to enter tissues, causing swelling. Like an army, there is also phagocyte recruitment that attracts immune cells to the site of infection to eliminate pathogens.

Then other components that come into action are the antimicrobial proteins which are a complement system where a group of proteins enhance the ability of antibodies and phagocytic cells to clear pathogens.  Added to that are the opsonization which means coating pathogens to make them more recognizable to phagocytes. That’s not all. There is this thing called Membrane Attack Complex (MAC). These form pores in the membranes of pathogens, leading to their lysis. Comes next the interferons which are proteins produced by virus-infected cells that help protect neighbouring cells from viral infection.

Next in line we have the adaptive immunity that involves specificity and memory. Here lymphocytes, the primary cells are involved in adaptive immunity, involving B cells that produce antibodies that bind to specific antigens. Upon activation, they differentiate into plasma cells that produce large quantities of antibodies which we shall classify them shortly.

The immunological system is also armed with memory B cells. These cells have memories that provide long-lasting immunity by remembering past infections. Comes another type or army – the T cells. They are involved in cell-mediated immunity. There are two main types, the helper T Cells (CD4+) where they activate B cells and other immune cells by releasing cytokines. The immune system has yet another type of army we call them as cytotoxic T Cells (CD8+). They directly kill infected or cancerous cells.

Having said all that, next comes the antigen presentation that is made of a major histocompatibility complex (MHC). These are molecules that present antigens on the surface of cells. Immunologists group them as MHC Class I, found on all nucleated cells, present antigens to cytotoxic T cells. MHC Class II are found on antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells, present antigens to helper T cells.

That’s not all. The immunological system also has the Clonal Selection and Expansion. When a lymphocyte recognizes its specific antigen, it undergoes clonal expansion, producing many identical cells that can respond to the pathogen. They have the effector cells that actively respond to the infection. The memory cells then provide a rapid and robust response if the pathogen is encountered again.

Having explained all that, comes the antibodies most people have heard of.

Antibodies have a structure that consists of variable regions that bind specific antigens and constant regions that determine the class of the antibody. Their functions are:

Neutralization that blocks pathogens or toxins from interacting with host cells. Opsonization that marks pathogens for phagocytosis. Complement Activation that triggers the complement system leading to pathogen destruction.

Agglutination then clumps pathogens together for easier removal. There are many types of antibodies. Antibodies, also known as immunoglobulins (Ig), play a crucial role in the immune defence against pathogens and abnormal cells. There are five main classes of antibodies, each with specific functions and characteristics:

Classes of Antibodies are:

IgG (Immunoglobulin G). They are the most abundant antibodies in the blood and extracellular fluid. They provide long-term protection and memory. They are capable of crossing the placenta to provide passive immunity to the foetus.

Involved in opsonization, neutralization of toxins and viruses, and activation of the complement system.

IgA (Immunoglobulin A):

Functions:

IgA are found in mucous membranes lining the respiratory and gastrointestinal tracts, as well as in saliva, tears, and breast milk. They protect the mucosal surfaces by preventing the attachment and entry of pathogens. They play a role in mucosal immunity.

IgM (Immunoglobulin M):

Functions:

IgM is the first antibody produced in response to an infection.

It is found in the blood and lymphatic fluid. It is effective at forming antigen-antibody complexes and activating the complement system. It plays a crucial role in the primary immune response.

IgE (Immunoglobulin E):

Functions:

IgE is involved in allergic reactions and responses to parasitic infections. It binds to allergens and triggers histamine release from mast cells and basophils. It mediates immediate hypersensitivity reactions.

IgD (Immunoglobulin D):

Functions:

IgD presents in small amounts in the blood and on the surface of B cells. It is involved in the activation and regulation of B cells during the immune response. Its precise role is less well understood compared to other antibody classes.

Antibody Subclasses. Some antibody classes have further subclasses that provide more specialized functions. For example, IgG Subclasses are:

IgG1: Most abundant subclass, effective in opsonization and complement activation.

IgG2: Involved in responses to bacterial polysaccharides.

IgG3: Highly effective in complement activation.

IgG4: Involved in responses to allergens and chronic infections, and less effective in complement activation.

IgA Subclasses:

IgA1: Found primarily in serum.

IgA2: Found primarily in secretions at mucosal surfaces.

Specific Antibodies:

In addition to the general classes and subclasses, there are specific antibodies used in clinical and therapeutic contexts. These are often monoclonal antibodies, designed to target specific antigens associated with diseases. Some notable examples include:

Rituximab (anti-CD20): Used to treat certain autoimmune diseases and cancers, particularly B-cell non-Hodgkin lymphomas.

Trastuzumab (Herceptin, anti-HER2/neu): Used to treat HER2-positive breast cancer.

Pembrolizumab (Keytruda, anti-PD-1): Used in cancer immunotherapy to block the PD-1 pathway and enhance the immune response against tumours.

Infliximab (Remicade, anti-TNF-alpha): Used to treat autoimmune diseases such as rheumatoid arthritis and Crohn’s disease.

Omalizumab (Xolair, anti-IgE): Used to treat allergic asthma and chronic spontaneous urticaria.

These monoclonal antibodies are specifically engineered to target particular molecules involved in disease processes, and they represent an important application of antibody technology in modern medicine.

Integration of Innate and Adaptive Immunity:

·         Cytokines and Chemokines: Small proteins released by cells that mediate and regulate immunity, inflammation, and haematopoiesis. They help in the communication between innate and adaptive immune responses.

·         Antigen-Presenting Cells (APCs): Such as dendritic cells and macrophages, bridge the innate and adaptive immune systems by presenting antigens to T cells.

The coordination and interplay between these various mechanisms ensure that the body can effectively detect, respond to, and remember pathogens, providing both immediate and long-term protection against infections.

We can see how wonderful our Immunological System works for us. In fact, all their components and subcomponents are active all the time, every second, every minute in our entire life defending us silently against infection without us knowing it.

And yet, doctors unnecessarily prescribe all those antibiotics for us for every infection, causing an abuse in antibiotics resulting in a lot of antibiotic strains of bacteria that have developed resistance to antibiotics. This resistance can be to a single antibiotic or multiple antibiotics, making infections caused by these bacteria more difficult to treat when in truth the body by itself can easily handle most of the infections.   

We shall talk about this in another article.

“A True Doctor is One Who Teaches, The Best Healer is Your Own Body” (Motto of my blog)

Lim ju boo