Methotrexate is a medication that can be used to treat various conditions, including rheumatoid arthritis, psoriasis, and cancer. The medication works by suppressing the immune system, which can help reduce inflammation and prevent the immune system from attacking healthy tissues [2].

Methotrexate affects the immune system by inhibiting the production of certain immune cells, such as T cells and B cells. This can reduce the overall activity of the immune system and make it less responsive to infections and other foreign invaders [3].

In children, methotrexate is often used to treat juvenile idiopathic arthritis (JIA). While the medication can be effective in reducing joint inflammation and preventing joint damage, it can also have side effects on the immune system. Children taking methotrexate may be more susceptible to infections, and it is important to monitor for signs of infection and take appropriate precautions [2].

Other potential side effects of methotrexate in children include gastrointestinal symptoms, such as nausea and vomiting, as well as liver toxicity and bone marrow suppression [1]. Regular monitoring of blood tests and liver function is typically recommended to monitor for these side effects [2].

In summary, methotrexate affects the immune system by suppressing the production of certain immune cells, which can reduce inflammation and prevent the immune system from attacking healthy tissues. In children, methotrexate may increase the risk of infections and can have other potential side effects, including gastrointestinal symptoms, liver toxicity, and bone marrow suppression. Regular monitoring is important to ensure the medication is being used safely and effectively [2][3].

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/METHOTREXATE
[2] https://www.versusarthritis.org/about-arthritis/treatments/drugs/methotrexate/
[3] https://www.ouh.nhs.uk/patient-guide/leaflets/files/13897Pmethotrexate.pdf