New results
A group of researchers from Paracelsus Medical University in Salzburg, Austria, have published their most recent results. In mouse models (mice that carry a human gene and express human protein) with grass pollen allergy, researchers have found that when these mice were exposed to an allergen, it lead to the development of new neurons – or nerve cells – and reduced activity of immune cells in the hippocampus of the brain.
Hippocampus is the part of the brain responsible for memory and learning. Worldwide, hay fever affects between 10-30 % of the population, and it usually occurs in spring, summer and early autumn. The condition arises when the body’s immune system becomes sensitised to a range of allergens and irritants, most commonly from grass, trees, and weeds. Symptoms of hay fever include runny or stuffy nose, itchy eyes, mouth or skin, sneezing and fatigue.
The Austrian researchers note that previous research has already indicated that allergic reactions may affect functions within the central nervous system (CNS) – especially functions related to memory and learning.
The researchers wished to investigate this association by assessing how an allergic reaction can affect the brains of mice with grass pollen allergy. The mouse models’ brains were then compared to those of mice that did not have a grass pollen allergy (the controls).
What do the results say?
The results showed that compared with the control mice, the brains of allergic mice showed greater neurogenesis in the hippocampus when exposed to grass pollen. In addition, researchers observed that an allergic reaction to grass pollen reduced microglia activity in the hippocampus of the mice. Microglia are the primary immune cells of the central nervous system, meaning that they are the brain’s first line of defence against pathogens.
In the light of these results, researchers say that they were surprised to find reduced microglia activity in the hippocampus due to an allergic reaction, partly because previous research have shown increased microglia activity in this brain region as a reaction to bacterial infections.
Researchers know that the immune system’s response in the body varies, depending on whether the cause is a bacterial infection or an allergic reaction. This means that the effect on the brain depends on the type of immune reaction in the body.
What this altering of the brain in mice with allergy means to the brain function is still unknown. Today, it is well-known that neurogenesis in the hippocampus normally declines with age, which contributes to memory-related disorders like Alzheimer’s disease. In the present study, the neurogenesis was increased and therefore, researchers hypothesise that this change may also have functional consequences on learning and memory. Further studies are required to examine this assumption.
In addition, researchers can now speculate whether the reduced activity of microglia in the hippocampus due to an allergic reaction could have harmful consequences, especially if the activity is reduced for long periods of time. Once again, further experiments are needed to understand the change and its consequences.
All in all, we now know that an allergic reaction affects the nerve tissue for example in the hippocampus, but it is still unclear exactly what this change means.
Sources:
http://www.medicalnewstoday.com/articles/312218.php
http://www.aaaai.org/about-aaaai/newsroom/allergy-statistics
