Most of these are commensals, and do us no harm. But that is because neutrophils keep them in check. However, heavy doses of radiation chemotherapy and many other forms of stress can reduce the numbers of neutrophils so that formerly harmless bacteria begin to proliferate. The resulting opportunistic infection can be life-threatening. However, their numbers increase sharply in certain diseases, especially infections by parasitic worms.
Eosinophils are cytotoxic, releasing the contents of their granules on the invader.
The number of basophils also increases during infection. Basophils leave the blood and develop into mast cells . Their granules contain histamine and when they discharge these are the site of infection, the histamine increases the blood flow to the area. Mast cells also play an important part in some allergies such as hay fever and an anaphylactic response to insect stings. Platelets Platelets are cell fragments produced from megakaryocytes .