A 13-month-old boy is brought to the clinic after repeated infections for the past 4 months, including otitis media, pneumonia, and erysipelas. Although his infections have been responsive to treatment, his father is concerned about the number of infections. The patient also has persistent diarrhea, and a recent stool antigen detection assay was positive for Giardia lamblia. An immunoglobulin panel demonstrates very low serum levels of all immunoglobulin types. Intradermal injection of Candida antigens results in a large indurated nodule within 48 hours. This patient's lymph nodes most likely lack which of the following structures?

Question

A 13-month-old boy is brought to the clinic after repeated infections for the past 4 months, including otitis media, pneumonia, and erysipelas.  Although his infections have been responsive to treatment, his father is concerned about the number of infections.  The patient also has persistent diarrhea, and a recent stool antigen detection assay was positive for Giardia lamblia.  An immunoglobulin panel demonstrates very low serum levels of all immunoglobulin types.  Intradermal injection of Candida antigens results in a large indurated nodule within 48 hours.  This patient's lymph nodes most likely lack which of the following structures?

Quizplus · Accepted Answer

11ec160b_37d1_cbe9_9249_296c0c469e87_MD0001_00 This patient's recurrent infections in the setting of intact T lymphocyte function (positive response to Candida antigens) and very low immunoglobulin levels suggest X-linked (Bruton) agammaglobulinemia (XLA). This condition results from a mutation in the Bruton tyrosine kinase gene that causes failure of bone marrow pre-B cells to develop into mature B lymphocytes. As a result, patients have absent or very low B lymphocytes in the peripheral blood and lymphoid tissues. In general, B lymphocytes aggregate in the cortex of lymph nodes to form lymphoid follicles. Primary follicles are dense and dormant; secondary follicles have a pale germinal center containing proliferating B cells in response to an antigenic stimulus. In XLA, primary lymphoid follicles and germinal centers do not form due to an absence of B cells. Lack of mature B lymphocytes also leads to inability to produce plasma cells, and patients therefore have absent or very low serum immunoglobulins. Recurrent infections typically begin once maternally derived antibodies wane (age 3-6 months), as seen here. (Choice B) The outer cortex is composed of primary and secondary lymphoid follicles (ie, B cell-rich regions), but it also contains prominent numbers of CD4+ T cells within the interfollicular regions (allowing for T-B cell interaction). In patients with XLA, the outer cortex is present but diminished. (Choice C) The paracortical zone lies internal to the cortex of the lymph node. This zone is populated primarily by T lymphocytes and dendritic cells. Dendritic cells present antigens collected from the blood and lymph to the T lymphocytes aggregated in this section of the node. This patient's positive reaction to Candida antigens (type 4 hypersensitivity) indicates intact T lymphocyte function. (Choices D and E) The subcapsular sinuses are found between the capsule and the cortex of the lymph node and are in direct communication with afferent lymphatic vessels. These sinuses are connected to cortical sinuses that line the trabeculae and penetrate through the cortex and paracortex to reach the medulla. From there, medullary sinuses drain into the efferent lymphatic channel. These structures are not affected in XLA. Educational objective: X-linked (Bruton) agammaglobulinemia is caused by a defect in B cell maturation, resulting in absent mature B cells and severely low immunoglobulin levels. T cell numbers and function remain intact. Due to the absence of B cells, primary lymphoid follicles and germinal centers do not form within lymph nodes. __________ References: X-linked agammaglobulinemia. (http://www.ncbi.nlm.nih.gov/pubmed/31751055)

A 13-Month-Old Boy Is Brought to the Clinic After Repeated