In infectious mononucleosis, the patient exhibits- Atypical lymphocytes in the circulating blood. - Antibodies to the EB Virus. - Increased heterophile antibody titre. The normal titre of agglutinins and hemolysins in human blood against sheep red blood cells does not exceed 1:8, but in infectious mononucleosis the titre may rise to 1:4096. This is referred to as positive Paul Bunnel test and is both characteristic and pathognomic of the disease.