Category Human Body

Your spleen’s main function is to act as a filter for your blood. It recognizes and removes old, malformed, or damaged red blood cells. When blood flows into your spleen, your spleen performs “quality control”; your red blood cells must pass through a maze of narrow passages. Healthy blood cells simply pass through the spleen and continue to circulate throughout your bloodstream. Blood cells that can’t pass the test will be broken down in your spleen by macrophages. Macrophages are large white blood cells that specialize in destroying these unhealthy red blood cells.

Your spleen also plays an important part in your immune system, which helps your body fight infection. Just as it detects faulty red blood cells, your spleen can pick out any unwelcome micro-organisms (like bacteria or viruses) in your blood.

When one of these invaders is detected in your bloodstream, your spleen, along with your lymph nodes, jumps to action and creates an army of defender cells called lymphocytes. Lymphocytes are a type of white blood cell that produces antibodies, special proteins that weaken or kill bacteria, viruses, and other organisms that cause infection. Antibodies and white blood cells also stop infections from spreading through the body by trapping germs and destroying them.

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T cells originate from haematopoietic stem cells which are produced in the bone marrow. Some of these multipotent cells will become progenitor cells that leave the bone marrow and travel to the thymus via the blood. In the thymus these cells mature: T cells are named after their thymus-dependent development.

T cells undergo a selection process in the thymus, which the majority of developing T cells (called thymocytes) will not survive. Thymocytes that interact with self-MHC molecules receive positive signals for survival, and thymocytes that have receptors to self-antigen molecules receive negative signals and are removed from the repertoire.

Each T cell will develop its own T cell receptor (TCR) that is specific for a particular antigen. T cells that survive thymic selection will mature and leave the thymus. They will circulate through the peripheral lymphoid organs, each ready to encounter a specific antigen and become activated. Once activated, the T cell will proliferate and differentiate into an effector T cell.

The thymus involutes as we age and so produces fewer naïve T cells over time. This means that older people have reduced T cell diversity, which contributes to the increased susceptibility to infections seen with age.

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Germs look for ways to get under your skin — literally. They could get in through a cut, ride in on something you ate, filter through the air, or wait on a coin for you to touch it and then rub your eyes.

Once inside, they start to breed. You’re infected, and it can make you feel sick.

Your immune system should know that there’s a problem. It reads a tell-tale “fingerprint” of proteins on the surface of cells, so it can tell the difference between your own cells and what shouldn’t be there. 

Your white blood cells aim to destroy the unwelcome guests.

They get their start in your bone marrow. They have a short life — ranging from a few days to a few weeks — so your body constantly makes more. There are different types, and they all have the same goal: to fight infection.

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Antibodies are passed from mother to baby through the placenta during the third trimester (last 3 months of pregnancy). This gives the baby some protection when they are born. The type and amount of antibodies passed to the baby depends on the mother’s own level of immunity.

During birth, bacteria from the mother’s vagina is passed on to the baby. This helps to build the colony of bacteria in the gut that contributes to their immunity.

After birth, more antibodies are passed on to the baby in colostrum and in breast milk. But babies’ immune systems are still not as strong as adults’. Premature babies are at greater risk of infection because their immune systems are even more immature and they haven’t had as many antibodies passed to them from their mothers.

Babies produce their own antibodies every time they are exposed to a virus or germ, but it takes time for this immunity to fully develop.

The passive immunity passed on from the mother at birth also doesn’t last long and will start to decrease in the first few weeks and months after birth.

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