The term INFECTION FIGHTERS can be broken down into two crossword solutions: SERA (4 letters) and WHITEBLOODCELLS (15 letters). SERA stands for 'serum antibodies, ' which are proteins produced by the immune system in response to a foreign substance, such as a virus or bacteria. White blood cells, also known as leukocytes, are a type of cell that helps the body fight off infections by attacking and destroying foreign substances. Together, these two components form the body's defense against infection.