A 22-year-old woman comes to the office due to 2 weeks of profound fatigue, which has prevented her from attending college classes. The fatigue was preceded by fevers and sore throat, but these have now improved. The patient is an exchange student from Turkey and has no prior medical conditions. She does not use tobacco, alcohol, or illicit drugs. Vital signs are within normal limits. Oropharyngeal examination shows no abnormalities. There are several enlarged lymph nodes posterior to the sternocleidomastoid muscle bilaterally. Cardiopulmonary examination is unremarkable. The spleen is palpable 1 cm below the left costal margin. No skin rashes or other lymphadenopathy is present. Peripheral blood evaluation shows increased numbers of abnormal white blood cells as shown in the exhibit.

The observed cytoplasmic granules of these cells are most likely to contain which of the following substances?

Question

A 22-year-old woman comes to the office due to 2 weeks of profound fatigue, which has prevented her from attending college classes. The fatigue was preceded by fevers and sore throat, but these have now improved. The patient is an exchange student from Turkey and has no prior medical conditions. She does not use tobacco, alcohol, or illicit drugs. Vital signs are within normal limits. Oropharyngeal examination shows no abnormalities. There are several enlarged lymph nodes posterior to the sternocleidomastoid muscle bilaterally. Cardiopulmonary examination is unremarkable. The spleen is palpable 1 cm below the left costal margin. No skin rashes or other lymphadenopathy is present. Peripheral blood evaluation shows increased numbers of abnormal white blood cells as shown in the exhibit.

The observed cytoplasmic granules of these cells are most likely to contain which of the following substances?

Quizplus · Accepted Answer

11ec160b_37d5_0043_9249_e16625ba6fd8_MD0001_00 This patient's peripheral blood smear reveals a reactive (atypical) lymphocyte. In contrast to normal lymphocytes, which are small, round, and have minimal cytoplasm, reactive lymphocytes are large, scalloped, and have abundant cytoplasm. Reactive lymphocytes are activated, pathogen-specific cytotoxic T cells and natural killer cells that form in response to certain intracellular infections (eg, HIV, cytomegalovirus, toxoplasmosis); they are particularly linked to infectious mononucleosis, a primary Epstein-Barr virus characterized by fever, pharyngitis, adenopathy, splenomegaly, and severe fatigue (as is likely in this patient). Reactive lymphocytes are effector cells that contain cytotoxic granules composed of perforin (creates holes in the infected cell's membrane) and granzymes (enter the cytoplasm of infected cells and trigger cell death), which are released in response to foreign antigens on the surface (MHC class I receptors) of infected host cells. (Choice A) Elastase breaks down collagen and is released by neutrophils and macrophages during acute inflammation. Neutrophils have multi-lobe nuclei and pinkish cytoplasm; macrophages have central round nuclei and abundant greyish, vacuolated cytoplasm. Neither typically has scalloped edges or abundant basophilic cytoplasm. (Choice B) Immunoglobulins are secreted by plasma cells, which have an eccentric nucleus, perinuclear paleness (large Golgi apparatus), and spoke-wheel chromatin. Although immunoglobins cannot typically be visualized on light microscopy, immunoglobulin inclusions can sometimes be seen in plasma cell malignancies such as multiple myeloma (characterized by anemia, hypercalcemia, bone pain, and renal insufficiency). (Choice C) Eosinophils generate and release major basic protein, which is the core constituent of eosinophilic granules; it acts as a cytotoxin and helminthotoxin and mediates epithelial damage, exfoliation, and bronchospasm in hypersensitivity diseases. Eosinophils have a bilobed nucleus and stain intensely pink. (Choice E) Ribosomes generate proteins from messenger RNA; they can be visualized by electron microscopy but usually cannot be seen on light microscopy. However, ribosomal aggregates can sometimes be seen as basophilic stippling in patients with thalassemia or alcoholism. (Choice F) Viral capsids are usually bound to viral genomes and shed in the cytoplasm prior to viral replication. This typically cannot be seen on light microscopy. Atypical lymphocytes are not infected by virus; they react to infected cells. Educational objective: Reactive (atypical) lymphocytes are activated, pathogen-specific cytotoxic T cells or natural killer cells that form in response to certain intracellular infections. In contrast to normal lymphocytes, reactive lymphocytes are large, scalloped, and have abundant cytoplasm. Reactive lymphocytosis is a diagnostic feature of infectious mononucleosis.

A 22-Year-Old Woman Comes to the Office Due to 2