The immune system has an incredibly adept system for killing invading organisms and protecting itself but when you are bitten by a tick and that tick transmits Lyme disease bacteria, the immune system response may not be as robust as we would like. The reason for this is twofold: tick saliva may confuse the immune system into ignoring the bacteria; the bacteria themselves may sufficiently resemble our own cells and go unnoticed. So what happens when the immune system mounts an attack on an invading organism and why does this lead to Lyme disease symptoms?
First Lines of Defence Against Lyme Disease
Our immune system is a complicated network that involves cells, tissues, and organs all working to defend the body against damage from invading organisms. Fungi, bacteria, parasites, and viruses are the usual suspects that can infect us and the human body is actually quite a hospitable place for many of these, assuming the microbes can avoid detection or replicate quickly enough to survive. The immune system has a two-pronged approach to its defence of the body, namely keeping organisms and viruses out or hunting them down and destroying them.
Immune System Cells
When bacteria, like Borrelia, do manage to infiltrate the body they will usually encounter antibodies called immunoglobulin A (IgA) as the first line of defence. Underneath the uppermost layers of skin are other immune cells such as macrophages, B cells, T cells, and then a range of cells that have no specific targets and form part of the innate immune system. These kinds of cells include phagocytes that consume bacteria and other invading organisms, natural killer T cells, and complement.
Why You Can be Reinfected with Lyme Disease
Some of the immune system cells are specifically created to fight certain bacteria and the body creates a memory bank of certain antigen-specific cells so that a quick response can be mounted if a person is infected with the same organism again; this is how vaccines work. Some microbes adapt too quickly, however, and so the body cannot always use the same antibody to counteract a bacterium that has mutated from one it has fought off before.
Lyme disease bacteria also undergo certain mutations that may confound the body’s defences meaning that a person can feasibly become reinfected with Lyme disease shortly after having been treated successfully with antibiotics. In fact, evidence suggests that many of those patients who have been labeled as having chronic Lyme disease are actually suffering from repeated reinfection.
Antibodies and How Lyme Disease Bacteria Hide
Antibodies and T cells are able to mount targeted attacks on bacterial cells and instigate a process that calls upon other cells such as lymphocytes to attack the bacteria. Most bacteria live between cells in the body and so are exposed to these antibodies which, once attached to the target, send out signals to draw phagocytes to destroy the organism. Viruses, unlike most bacteria and parasites, have to enter the cells to survive, and Lyme disease bacteria are also thought to do this by switching from a spirochaetal form to a cystic form and by creating biofilms. By hiding in the cells these organisms need a different kind of system to eradicate them and, unfortunately, the host cells will also be destroyed in this process in most cases.
The Lyme Disease Rash and Swelling
The process of defending the body against invading organisms will usually mean that immune system cells have to rush to a specific site, such as where a tick bite has occurred, in order to attack the bacteria before it has a chance to reproduce and spread through the whole body. This can cause localized swelling in an area, and the resulting erythema migrans that is seen in Lyme disease.
Why Lyme Disease Symptoms Vary
As the bacteria enter general circulation they may find tissues that are already weak as these are easier to colonize due to impaired cell membrane defences. This is why many people who are predisposed to heart conditions find that Lyme disease can exacerbate symptoms, or why those with existing joint problems have more severe Lyme arthritis than those with previously healthy joints. Because Borrelia can invade practically any tissue in the body and trigger an immune system response in the joints, heart, liver, brain, or other organ or system, the symptoms of Lyme disease are varied, unpredictable, and often mimic other diseases, thus confusing and delaying diagnosis.