Tissue Optics and Photoimmunology

Abstract

Whenever an organism, organ, or cell is exposed to UV or other optical radiation, the response, or lack of response, depends to some extent on the optical properties of the exposed tissues. Delineating the exact nature of this dependence is both necessary and instructive in experimental work. For example, cells in tissue culture are more sensitive to loss of viability by exposure to 254-nm radiation when they are adherent and flattened against their substrate than when they are rounded. In the latter case, a greater pathlength of cytoplasm intervenes between the plasma membrane and nucleus, resulting in more effective shielding of the DNA chromophore by cytoplasmic absorption and scattering. One can, in fact, use this to measure the optical absorbance of living cytoplasm.¹ Thus, one of the first concerns in the study of tissue optics is to ascertain the fraction of incident radiation at specified wavelengths that reaches important chromophores and initiates responses, or perhaps for the immunologist, that reaches the tissues and cells mediating immune responses.