Study of lymphocyte subpopulations and T-lymphocyte activation index in patients with suspected secondary immunodeficiencies

Medical Review (Med. pregled), 2026, 62(2), 29-36.

M. Petrova, E. Kurteva, E. Ivanova-Todorova

Laboratory of Clinical Immunology, University Hospital “Sv. Ivan Rilski”
Department of Clinical Immunology, Medical Faculty, Medical University of Sofia

Abstract: Secondary immunodeficiencies (SIDs) are more frequent than primary immune defects and can arise from various external factors such as chronic infections, immunosuppressive therapy, or malnutrition. The functional and quantitative assessment of immune competence is typically performed using lymphocyte immunophenotyping and the phytohemagglutinin (PHA) proliferation test. Despite their broad use, few studies have assessed how often abnormalities in these tests occur among patients suspected of SID. Aim: This study aimed to evaluate the frequency and nature of alterations in immunophenotyping and PHA test results among patients with suspected secondary immunodeficiencies. Materials and Methods: We conducted a retrospective analysis of 85 patients (age range: 3-79 years) examined in the Laboratory of Clinical Immunology at University Hospital “Sv. Ivan Rilski” between February 2024 and August 2025. Each patient underwent immunophenotyping of lymphocyte subpopulations (T, B, and NK cells) using flow cytometry and a PHA activation test to determine T-cell proliferative capacity. Results: Abnormalities in PHA index were observed in 42 patients (49.4%), while 34 patients (38.8%) showed deviations in immunophenotyping. Sixteen and a half percent of all patients (n=14) exhibited combined alterations in both tests, with T-cell and NK-cell populations being most frequently affected. Isolated abnormalities in immunophenotyping occurred in 23.5% of patients, most commonly involving NK cells (CD16+/CD56+). Conclusion: Nearly half of the examined patients demonstrated some degree of immune dysfunction, with the most frequent changes affecting T- and NK-cell subsets. The combined use of immunophenotyping and PHA testing provides a more comprehensive evaluation of cellular immune competence and may aid in identifying secondary immunodeficiencies related to chronic infections or immune dysregulation.

Key words: secondary immune deficiencies, flow cytometry

Address for correspondence: Meri Petrova, MD, e-mail: meri.petrova1234@gmail.comg