The cause of pain is not inflammation, but bacteria
Everything hurts because of bacteria
Polina Rozentsvet, <url>Many bacterial infections are accompanied by pain.
These are meningitis, caries, diseases of the genitourinary tract and intestines and other similar ailments. Experts have always believed that this pain is caused by inflammation – an inevitable consequence of the immune system's response to infection. Indeed, the place where the germs got into is always red and swollen. But it turned out that everything was wrong. According to experts at Boston Children's Hospital, the pain is caused by the bacteria themselves, directly acting on sensitive neurons. Moreover, excited pain neurons do not stimulate, but suppress the immune response and inflammation. The results of the study are published in the journal Nature: Bacteria activate sensory neurons that modulate pain and inflammation (see the popular retelling in a press release, Boston Children's Hospital Bacteria make us feel pain... and suppress our immune response – VM).
Scientists have investigated the molecular mechanism of pain that occurs when infected with Staphylococcus aureus aureus. It is one of the most common pathogens of hospital infections, pneumonia and sepsis, the cause of abscesses and other painful pathologies. Mice were injected with bacteria in the hind leg, and after an hour their sensitivity to touch, heat and cold increased, after six hours it reached a peak, after a day it passed. Meanwhile, the tissue on the paw turned red and swelled only two or three days after infection, then the mice developed a second surge of pain sensitivity, weaker. So the researchers found that the pain is not associated with inflammation, but with the reproduction of bacteria, and the strength of the pain depends on the number of live staphylococci.
Pain is caused by two types of compounds that S.aigeis synthesizes. First of all, these are N-formyl peptides that interact with the receptors of pain neurons and increase their sensitivity to mechanical stimuli. The second class of substances are pore–forming toxins (alpha-toxins). They are embedded in the membrane of the neuron and create pores in it, through which calcium ions leave the cell – a pain signal. The result was quite unexpected, but another conclusion surprised the researchers even more: pain neurons activated by staphylococcus inhibit the activity of the immune system.
We used to think that pain is an alarm signal that mobilizes all the forces of the body to fight danger, in this case, infection. And everything, it turns out, is the opposite: pain suppresses the immune response, and does not stimulate it.
Researchers have discovered two mechanisms of fighting the immune system. First, pain neurons affect the first echelon of the body's defense – the innate immune response. It begins with the fact that neutrophils and macrophages flock to the source of infection. Staphylococcus–activated pain neurons secrete proteins that noticeably reduce the influx of these cells and prevent macrophages from synthesizing tumor necrosis factor - the main signaling molecule that triggers a further immune response.
Next, bacterial cells enter the lymph nodes, where they are met by T- and B-lymphocytes, which create a second wave of immune response. However, activated pain neurons prevent the migration of T and B cells to the lymph nodes. The researchers worked with transgenic mice whose pain neurons do not secrete calcium in response to bacterial infection. In such mice, the infected area swelled much more, and the lymph nodes contained more T and B cells. That is, with the "disabled" pain neurons, the infection itself proceeded almost painlessly, and the immune response to it was stronger.
The data obtained by American researchers make us take a different look at the nature of painful infectious diseases. When creating painkillers, it is necessary to think about how to suppress the development of the pathogen, and not an inflammatory or immune reaction. If we manage the pain in infected tissues, we can block the effect of pain neurons on the immune system.
Portal "Eternal youth" http://vechnayamolodost.ru22.08.2013