The body’s defence force

THERE IS no way to avoid it, everywhere around us is covered in germs. Bacteria and viruses are all around us in the air and on most surfaces, and these include germs such as bacteria, viruses, and fungi, and toxins; chemicals made by microbes.

So why are you not sick all the time? The reason is that your immune system protects you. The immune system is made up of different organs, cells, and proteins that work together. It is your body’s natural defences against illness, creating antibodies that break down invaders and help the body function.

MEMORY CELLS

According to Dr Shanique Hibbert, medical doctor at Thomas Medical Centre, the immune system keeps a record of every microbe it has ever defeated, in types of white blood cells (B-lymphocytes and T-lymphocytes) known as memory cells. This means it can recognise and destroy the microbe quickly if it enters the body again, before it can multiply and make you feel sick.

“Some infections, like the flu and the common cold, have to be fought many times because so many different viruses or strains of the same type of virus can cause these illnesses. Catching a cold or flu from one virus does not give you immunity against the others,” she said.

Dr Hibbert said there are two functional divisions to the body’s immune system – the innate immune system and the acquired immune system.

“The innate immune system is your rapid-response system. It is the first to respond when it finds an invader. It is made up of the skin, the eye’s cornea, and the mucous membrane that lines the respiratory, gastrointestinal, and genitourinary tracts. These all create physical barriers to help protect your body. They protect against harmful germs, parasites such as worms, or cells such as cancer,” Dr Hibbert said.

INVADER

The innate immune system is inherited and is active from the moment you are born. “When this system recognises an invader, it goes into action right away. The cells of this immune system surround and cover the invader. The invader is killed inside the immune system cells called phagocytes,” Dr Hibbert said.

The acquired immune system, with help from the innate system, makes special proteins called antibodies to protect your body from a specific invader. “These antibodies are developed by cells called B lymphocytes after the body has been exposed to the invader. The antibodies stay in your body. It can take several days for antibodies to form; however, after the first exposure, the immune system will recognise the invader and defend against it,” Dr Hibbert said.

“The acquired immune system changes during your life. Immunisations train your immune system to make antibodies to protect them from harmful diseases,” she added.

All immune cells come from precursors in the bone marrow and develop into mature cells through a series of changes that can occur in different parts of the body. These areas include the skin, bone marrow, bloodstream, thymus, lymphatic system, lymph nodes, spleen and mucosal tissue.

RESPONDERS TO INFECTION

“The skin is usually the first line of defence against microbes. Skin cells produce and secrete important antimicrobial proteins, and immune cells can be found in specific layers of skin. While the bone marrow contains stems cells that can develop into a variety of cell types that are important first-line responders to infection,” Dr Hibbert said.

Immune cells constantly circulate throughout the bloodstream, patrolling for problems. When blood tests are used to monitor white blood cells, another term for immune cells, a snapshot of the immune system is taken. If a cell type is either scarce or overabundant in the bloodstream, this may reflect a problem.

The lymphatic system is a network of vessels and tissues composed of lymph, an extracellular fluid, and lymphoid organs, such as lymph nodes. “The lymphatic system is a conduit for travel and communication between tissues and the bloodstream.

Immune cells are carried through the lymphatic system and converge in lymph nodes, which are found throughout the body,” Dr Hibbert said.

LYMPH NODES

Lymph nodes are a communication hub where immune cells sample information brought in from the body. “For instance, if adaptive immune cells in the lymph node recognise pieces of a microbe brought in from a distant area, they will activate, replicate, and leave the lymph node to circulate and address the pathogen. Thus, doctors may check patients for swollen lymph nodes, which may indicate an active immune response,” Dr Hibbert said.

The spleen is an organ located behind the stomach. While it is not directly connected to the lymphatic system, it is important for processing information from the bloodstream. “Immune cells are enriched in specific areas of the spleen, and upon recognising blood-borne pathogens, they will activate and respond accordingly,” she said.

Mucosal surfaces are prime entry points for pathogens, and specialised immune hubs are strategically located in mucosal tissues like the respiratory tract and gut. “For example, Peyer’s patches are important areas in the small intestine where immune cells can access samples from the gastrointestinal tract,” Dr Hibbert said.

The immune system is a complex system that is vital for survival. When the body faces harmful invaders, such as a virus or a splinter in the finger, it launches an attack to destroy the pathogens. People are born with some types of immunity, but exposure to diseases and vaccinations can also help boost the body’s defences.

Some people have a weakened immune system because of a health issue or medication use. A doctor can advise on how to protect a person’s health when living with a weakened immune system.

keisha.hill@gleanerjm.com