You will not go through immigration at either PIT or JFK: the United States does not have outbound immigration inspections. Your travel documents will be inspected by your airline(s) to ensure that you are eligible to be admitted to India.
As for security, if there is only one security checkpoint at JFK's terminal 8 (and I believe there is only one), and if you never leave the secure area between flights, then you will only pass through a security checkpoint at PIT. If you have to leave the secure area at JFK to check in for your flight to India, then you will have to re-clear security at Terminal 8.
You will not go through