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441a) The differential blood count results shown in the table are from a 44-year-old man with human immunodeficiency virus (HIV). Flow cytometric analysis of the same blood sample showed that CD4⁺ T cells represent 2% of all lymphocytes. Which one of the following is the CD4⁺ T-cell count of this patient?

Test Result Reference Range Units

WBCs 4.5 3.5-9.1 ×10⁹/L

Neutrophils 51 40-70 %

Lymphocytes 37 20-50 %

Monocytes 10 4-8 %

Eosinophils 2 0-6 %

Basophils 1 0-2 %

Test	Result	Reference Range	Units
WBCs	4.5	3.5-9.1	×10⁹/L
Neutrophils	51	40-70	%
Lymphocytes	37	20-50	%
Monocytes	10	4-8	%
Eosinophils	2	0-6	%
Basophils	1	0-2	%

33 × 10⁶/L. 740 × 10⁶/L. 90 × 10⁶/L. There is insufficient information to determine the CD4⁺ T-cell count.

441b) Flow cytometric analysis of this patient’s peripheral blood identified a subpopulation of CD3⁺ CD4– CD8– T cells, which accounted for 10% of the lymphocytes. Which one of the following do these cells most likely represent?

Natural killer (NK) cells. Helper T cells showing human immunodeficiency virus (HIV)-induced downregulation of CD4 expression. Gamma/delta T cells. Immature T cells.

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• The significance of CD4⁺ T-cell (helper) counts in monitoring progression to acquired immunodeficiency syndrome (AIDS) and response to highly active antiretroviral therapy (HAART) in patients with human immunodeficiency virus (HIV):

○ HIV-1 and HIV-2 retroviruses are cytotropic for CD4⁺ T lymphocytes (and other cells, such as macrophages, monocytes, and central nervous system microglial cells) and are responsible for direct killing of infected cells and indirect killing of bystander cells.

○ Progression to AIDS is accompanied by a marked decrease in the number of helper T cells and an imbalance of CD4⁺ helper/CD8⁺ T-cytotoxic cells.

• Applications of the lymphocyte subset analysis using flow cytometry:

○ Detection of immunodeficiency diseases

○ Abnormal percentages and absolute values of lymphocyte subsets can be seen in patients with immunodeficiency diseases, such as DiGeorge syndrome, major histocompatibility complex (MHC) class II deficiency, and ζ-chain–associated protein kinase 70 (ZAP-70) deficiency.

○ Monitoring of the effect of lymphocyte-depleting agents, such as thymoglobulin, alemtuzumab (Campath), and rituximab, in transplant recipients and patients with hematologic malignancies

○ Immune reconstitution studies after stem cell transplantation

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Clinical Pathology: General Principles, Hematology & Coagulation, Immunology & Histocompatibility, Urinalysis, Body Fluids, Clinical Microscopy, Genetic Testing

441b) Flow cytometric analysis of this patient’s peripheral blood identified a subpopulation of CD3+ CD4– CD8– T cells, which accounted for 10% of the lymphocytes. Which one of the following do these cells most likely represent?

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441b) Flow cytometric analysis of this patient’s peripheral blood identified a subpopulation of CD3⁺ CD4– CD8– T cells, which accounted for 10% of the lymphocytes. Which one of the following do these cells most likely represent?