Characterization of factors inducing apoptosis in thymocytes of mice bearing a transplantable T-cell lymphoma of spontaneous origin

It has been observed that the progressive ascitic growth of a transplantabl e T-cell lymphoma of spontaneous origin in murine host, designated as Dalto n's lymphoma (DL), induces inhibition of various immune responses and is as sociated with an involution of thymus accompanied by a massive depletion of the cortical region and alteration in the distribution of thymocytes cause d by induction of apoptosis with a decrease of CD4(+)CD8(+), CD4(+)CD8(-) a nd CD4(-)CD8(+) thymocytes. Here, we report that serum of DL-bearing mice c ontains soluble factors capable of inducing thymocyte apoptosis, the effect iveness of which increases with the progression of tumor growth. A decline of essential cytokines and hormones in the body due to their depletion by D L cells, which being a T-cell phenotype may have similar growth factor requ irements, is ruled out by our results, suggesting additional apoptosis-indu cing factors to be present in the tumor serum. Partial characterization of the serum to identify the biochemical nature of the putative serum-borne ap optosis inducing factor(s) showed that the same was proteinaceous. Further analysis of the sera of normal and DL-bearing mice by gel filtration using fast protein liquid chromatography (FPLC) and by sodium dodecyl sulfate-pol yacrylamide gel electrophoresis (SDS-PAGE) revealed that protein profile in the mio sera differed quantitatively as well as qualitatively. FPLC analys is could resolve six peaks in both the sera, out of which the peak containi ng protein(s) in the range of MW 35 kD showed a higher magnitude and apopto tic activity followed by peaks containing proteins of MW in the range of 67 and 116 kD respectively as compared to that of the corresponding peaks in the normal serum. These observations were also confirmed by SDS-PAGE, with the resolution of additional proteins in the range of 25-26 kD which were f ound to be absent in normal serum. Further, the paper discusses different p ossible factors that could be associated with the progression of DL growth.