Comparison of modulation interference microscopy, DNA spectrometry, DNA cytometry, and flow cytofluorimetry in the assessment of phytohemagglutinin-induced activity of human blood lymphocytes

Rationale: The study of the structural particulars and functional state of immune cells and primarily lymphocytes is of great importance for both fundamental and clinical medicine. It requires the development of simple and reliable analytic methods that would allow for fast and effective real-time assessment of cell activity.

Aim: To evaluate the effectiveness of the interference microscopy compared to DNA spectrometry, DNA cytometry, and flow cytometry with an internalized fluorescent label CFSE (carboxyfluorescein succinimidyl ester) in the assessment of PHA-induced proliferation of human blood lymphocytes.

Materials and methods: Phytohemagglutinin (PHA)-induced proliferative activity of blood lymphocytes from 10  healthy volunteers was studied with various methodological strategies. Blast transformation of lymphocytes was induced by their incubation for 5 days with PHA 5 μg/mL. The cell proliferative activity was assessed as follows: 1) by DNA spectrometry at 260/280 nm using Tecan Infinite 200  Pro with a  specialized NanoQuant Plate™; 2)  by cytophotometry followed by cell distribution analysis assessing deoxyribonucleic acid (DNA) content after staining with Felgen's dye with an imaging system based on an Olympus BX41 light microscope with a ProgRes CF camera; 3) by flow cytometry using an internalized fluorescent label CFSE; the analysis was performed with a BD FACS Calibur flow cytometer; 4) by measurement of the lymphocyte interference profile with a  modulation interference microscope MIM-340 (Schwabe, Russia). The functional activity of the nucleus (FAN) was determined and used as a criterion for assessment of the lymphocyte functional state.

Results: Incubation of lymphocytes with PHA led to an increase in the linear size by 22.2±2.8%, a  decrease in phase height by 46.3±4.7% (p=0.019), and an increase in FAN by 75.9±9.4%, vs control (p=0.046). As measured by isolated DNA spectroscopy, PHA stimulation of lymphocytes was associated with an increase in the amount of DNA by  55% vs baseline (409.8±22.3  ng/μL and 264.3±25.0  ng/μL, respectively, p=0.049). Felgen's reaction revealed that the proportion of nuclei containing more than 2n DNA was 2% in the control cells and 14.8% in the PHA-activated lymphocytes, with a  difference between the groups of 12.8%. CFSE staining with subsequent incubation and assessment by flow cytofluorimetry demonstrated an increase in the percentage of proliferating cells from 1.68±0.9% in the control to 55.56±5.6% (p=0.00068) in the mitogen-stimulated sample.

Conclusion: Modulation interference microscopy does not require the sample preparation and demonstrated comparable and even higher effectiveness compared to conventional methods for assessment of lymphocyte activity. At the same time, it allows for evaluation of the lymphocyte functional state in real time in the process of cultivation. This opens ample opportunities for evaluation immune cells for research and diagnostic purposes.