<prompt> A 23-year-old male presents with fever and cervical lymphadenopathy. The peripheral smear shows the following finding. Diagnosis isAMLALLInfectious mononucleosisNone of the above  <response>: Infectious mononucleosis Causative agent: Ebstein Barr virus HHV-4Mode of transmission: Direct contact with human secretions, most often by saliva Infected cells: Epithelial cells and B cells in the oropharynxEBV infects B cells through C3d complement receptor CD21 for which the co-factor used is MHC-II.By age of 3 years, about 100 of children have positive serological findings for EBV. But not all those infected individuals acquire the disease.EBV replicates in B cells, inducing expression of viral capsid antigen VCA, membrane antigen MA, early antigen EA, EBV nuclear antigens EBNA, and lymphocyte-detected membrane antigen LYDMA.Antibodies formed against these antigens were called heterophil antibodies which play a role in containing the infectionIncubation period: 2 to 5 weeks Triad of symptoms: Fever, pharyngitis, and cervical generalized lymphadenopathyPeripheral blood: Shows atypical lymphocytes which are T cell type however EBV affects B cells with abundant pale blue cytoplasm, large nuclei and conspicuous nucleoli called Downey cells Paul bunnel test: Agglutination of sheep erythrocytes by patients serum. Beef erythrocytes specific for infectious mononucleosis and guinea pig kidney are also used. Monospot test: Most sensitive test in which agglutination was formed between horse erythrocytes and patients serum.Serology: To detect EBV specific antibodies VCA IgM, VCA IgG, EA and EBNA.Ref: Iochims lymph node pathology p78 