Date of Award
5-1996
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Medical
First Advisor
James J. Smith
Second Advisor
Lyle H. Hamilton
Third Advisor
William J. Stekiel
Abstract
Although the process of phagocytosis has been widely investigated, Kupffer cell activity has been given the least attention even though in its in vivo activity is prominent.
The mechanism by which the phagocytic cell distinguishes a native from a foreign particle is not understood. The physical factors of surface charge and surface tension have been suggested to be important in phagocytosis; more recently metabolic factors have also been implicated in this process. The nature of the attachment of the particle onto the cell membrane of the phagocyte and the means by which this attachment initiates phagocytosis are both unknown. The present study was undertaken to evaluate the relative contribution of surface chage and surface tension of the particle and later, to ascertain the effects of Kupffer cell stimulation and depression on phagocytosis.
The primary approach used in these studies was the perfusion of polystyrene latex, PSL, (1.305 u in diameter) through the in situ rat liver. The PSL surface was modified by adsorption of either acidic or
basic gelatin or gum arablc. Using concentration ranges of 8 x 10-3 to 10-5 gm/100 ml of these coating agents resulted in percentage extractions of particles by the liver which varied between 12% to 100%. Zeta potential measurements indicated a heterogeneity of surface
coatings for the particle populations perfused. The percentage extractions were linearly related to the mean zeta potentials of the gelatin-coated PSL and likewise for the gum arabic-coated particles perfused; however, no relationship was apparent between the absolute mean zeta potentials and the percentage extractions.
The non-ionic detergents Triton X-100 and Triton X-205 were also used to modify the PSL surface. lnhibition of particle extraction occurred with detergent concentrations greater than 10-2 gm/100 ml. No
relationship was apparent between the zeta potential of the PSL particles or surface tension as measured at the liquid-air interface and the percentage extraction.
The results of these experiments do not support the contention that either surface charge or surface tension exerts a significant influence on PSL particle recognition and phagocytosis.
intravenous injection of several substances is known to stimulate or depress RES activity after a time lapse of several hours. Our results indicate that Zymosan, triolein and olive oil directly stlmulate, while ethyl stearate directly depresses Kupffer cell activity. This suggests that these substances. at least in part, manifest their in vivo activity independent of scrum opsonins.
It has been reported by others that the osmolarity of a suspension medium affects the phagocytic activity of leukocytes. Perfusion of the livers with hypotonic NaCl solutions enhanced, while hypertonic solullons depressed phagocytosis. Our results therefore indicate a similar effect on rat liver Kupffer cells.
Though chloride ion exerted no specific action on the Kupffer cell membrane, phosphate ion enhanced phagocytosis, its effect being dependent on the duration of exposure of the cell to this ion and independent of solution osmolarity. Such an effect may be related to the metabolic activity of the cell associated with phagocytosis.
These studies have shown that the nature of both the PSL particle surface and phagocytic Kupffer cell are important in the recognition and discrimination of foreign particles. It is unlikely, however, that recognition and ingestion depend primarily on either surface charge or surface tension.