Research paper
Selective mitomycin C and cyclophosphamide induction of apoptosis in differentiating B lymphocytes compared to T lymphocytes in vivo

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Abstract

Differentiating B and T lymphocytes differ in sensitivity to a number of environmental toxins and anticancer agents. B lymphocytes are susceptible and T lymphocytes resistant to killing by cyclophosphamide (Cy) metabolites capable of forming DNA interstrand cross-links. However, the mechanisms responsible for the rapid killing and loss of bursal-resident B lymphocytes are unknown. Therefore, we investigated the cellular mechanisms of selective toxicity of two cross-linking drugs, mitomycin C (MMC) and Cy, towards differentiating B and T lymphocyte populations using the chicken embryo model system. Viability of bursal-resident B lymphocytes (bursacytes) decreased starting at 5 h post exposure (PE) to MMC, and was maximally reduced by 71.6% by 10 h PE at the highest dose examined (9.0 μg MMC/g). Dose-dependent increases in the percentage of apoptotic bursacytes were observed as early as 5 h PE, and increased to 72% by 10 h PE. This was accompanied by reductions in bursacyte numbers. Cy also induced apoptosis in bursacytes. In contrast, thymus-resident lymphocytes (thymocytes) were much more resistant to the toxic effects of MMC and Cy. Viability of thymocytes was reduced by only 10% in the 9.0 μg/g MMC treatment group. In addition, the percentage of thymocytes engaged in apoptosis was much lower than that for bursacytes. MMC induced modest cell cycle inhibition in bursacytes and thymocytes. These data strongly suggest that MMC- and Cy-induced diferential toxicity involves primarily early and extensive triggering of apoptosis in differentiating B lymphocytes, leading to rapid reduction of lymphocyte numbers in the embryonic bursa.

Keywords

Mitomycin C
Cyclophosphamide
B and T lymphocytes
Apoptosis

Abbreviations

ANOVA
analysis of variance
BLL
B lineage lymphocyte
Cy
cyclophosphamide
DI
days of incubation
FITC
fluorescein isothiocyanate
G-PBS
PBS and goat serum
ICL
interstrand cross-links
MMC
mitomycin C
PE
post-drug exposure
PBS
phosphate buffered saline
PI
propidium iodide
TCDD
2,3,7,8-tetrachlorodibenzo-p-dioxin
TLL
T lineage lymphocyte

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