Page 367 - Textbook of Pathology, 6th Edition

and appearance in blood of atypical ‘mononucleosis cells’. 4. The proliferation of these cells is responsible for 351
The pathogenesis of these pathologic features is outlined generalised lymphadenopathy and hepatosplenomegaly.
below: 5. The sore throat in IM may be caused by either necrosis of
1. In a susceptible sero-negative host who lacks antibodies, B cells or due to viral replication within the salivary epithelial
the virus in the contaminated saliva invades and replicates cells in early stage.
within epithelial cells of the salivary gland and then enters B Besides the involvement of EBV in the pathogenesis of
cells in the lymphoid tissues which possess receptors for EBV. IM, its role in neoplastic transformation in nasopharyngeal
The infection spreads throughout the body via bloodstream carcinoma and Burkitt’s lymphoma is discussed in
or by infected B cells. Chapter 8 and diagrammatically depicted in Fig. 14.8.
2. Viraemia and death of infected B cells cause an acute
febrile illness and appearance of specific humoral antibodies Clinical Features
which peak about 2 weeks after the infection and persist
throughout life. The appearance of antibodies marks the The incubation period of IM is 30-50 days in young adults,
disappearance of virus from the blood. while children have shorter incubation period. A prodromal
3. Though the viral agent has disappeared from the blood, period of 3-5 days is followed by Frank clinical features
the EBV-infected B cells continue to be present in the lasting for 1-3 weeks, and subsequently complete recovery CHAPTER 14
circulation as latent infection. EBV-infected B cells undergo occurs after 2 months. The usual clinical features are as
polyclonal activation and proliferation. These cells perform two under:
important roles which are the characteristic diagnostic 1. During prodromal period (first 3-5 days), the symptoms
features of IM: are mild such as malaise, myalgia, headache and fatigue.
i) They secrete antibodies—initially IgM but later IgG class
antibodies appear. IgM antibody is the heterophile anti- 2. Frank clinical features (next 7-21 days) commonly are
sheep antibody used for diagnosis of IM while IgG fever, sore throat and bilateral cervical lymphadenopathy.
antibody persists for life and provides immunity against Less commonly, splenomegaly (50% patients), hepatomegaly
re-infection. (10% cases), transient erythematous maculopapular eruption
ii) They activate CD8+ T lymphocytes— also called cytotoxic on the trunk and extremities, and neurologic manifestations
T cells (or CTL) or suppressor T cells. CD8+ T cells bring are found. Pneumonia and cardiac involvement are
about killing of B cells and are pathognomonic atypical infrequent. One of the complications of IM is proneness for
lymphocytes seen in blood in IM. splenic rupture due to splenitis. Disorders of Leucocytes and Lymphoreticular Tissues

Figure 14.8 The role of EBV in the pathogenesis of infectious mononucleosis, nasopharyngeal carcinoma and Burkitt’s lymphoma.