Simplify the following text for a Grade 10 native English-speaking person.
Original: Following maturation , the lymphocytes enter the circulation and peripheral lymphoid organs ( e.g. the spleen and lymph nodes ) where they survey for invading pathogens and\/or tumor cells .
Simplified: After they mature , the lymphocytes enter the circulation and lymphoid organs ( e.g. the spleen and lymph nodes ) where they are able to sense invading pathogens and tumor cells .