The picture below is from a 15-year-old boy that has been co…

The picture below is from a 15-year-old boy that has been complaining of a sore throat for the last two weeks.  He has a WBC count of 25,000/ul, has 25% of the cells shown below and his heterophile antibody test is positive.  Based on the aforementioned data, what is the most probable diagnosis?