Hi Shravan,
Unfortunately this is a question that is impossible to give a specific answer to. Low white blood cells can be due to many things, including infection, cancer, lupus, and different medications. The treatment is dependent on what is causing the decreased blood count, so it should be followed up with a doctor to follow this up. There is no specific diet that will increase the white blood cells, but havy a healthy diet will always help with general health.
Good luck,
JMK MD