Y. Takai et al., LIPID STRUCTURE OF CYTOTOXIC GRANULES IN LIVING HUMAN KILLER T-LYMPHOCYTES STUDIED BY RAMAN MICROSPECTROSCOPY, Biochimica et biophysica acta (G). General subjects, 1335(1-2), 1997, pp. 199-208
The structures of cytotoxic granules in interleukin-2-activated human
killer T lymphocytes have been investigated by Raman microspectroscopy
at a single cell level. The Raman spectra of granules share a common
feature that lipid Raman bands are much stronger than the Raman bands
due to protein, indicating that one of the main components of the gran
ule is lipid. To analyze the lipid structures of individual granules,
relationships between Raman spectra and structures have been examined
for a series of triacylgycerols with varied degrees of acyl chain unsa
turation. Analysis based on the relationships shows that the granulous
lipid is characterized by a high content of cis C=C bond, which range
s from about 1.5 C=C bonds per acyl chain in isolated minor granules a
nd to about 2.2 C=C bonds in clustering major granules. The highly uns
aturated lipid of major cytotoxic granules is in sharp contrast to the
moderately unsaturated (about one C=C bond per acyl chain) plasma mem
brane lipid. The large difference in lipid unsaturation between the gr
anule and plasma membrane may have relevance to the role of granulous
lipid in packaging cytotoxic proteins inside the granule and preventin
g them from attacking the killer lymphocyte itself.