Vitamin A: probe of immune complement reactions. II. Enhancement of human complement hemolysis

Anti-infective properties of vitamin A

1. Six months after feeding a vitamin A free diet the liver content of mice was markedly reduced but not yet completely exhausted. These vitamin A deprived mice were either immunized with sheep erythrocytes or infected with Listeria monocytogenes. In comparison to normal control mice no significant difference ws observed. This indicates that neither the immune system nor the mononuclear-phagocytic system was involved. 2. Mice treated with a high dose of vitamin A showed increased antibody production against sheep erythrocytes and also increased resistance against infection with L. monocytogenes. These experimental findings indicate a stimulatory effect on the immune system and the mononuclear phagocytic system. As a conclusion it is deduced that the term "anti-infective vitamin" does not hold absolutely true for vitamin A, although certain anti-infective properties cannot be denied.

Vitamin A in liposomes. Inhibition of complement binding and alteration of membrane structure

Incorporation of vitamin A aldehyde (retinal) into liposomes had an inhibitory effect on the amount of human complement protein bound in the presence of specific antiserum. The total membrane-bound protein was directly measured on liposomes which were washed after incubation in antiserum and fresh human serum (complement). At every concentration of complement, decreased protein binding was found with liposomes which contained retinal. Binding of the third component of complement (C3) was also measured directly on washed liposomes and was found to be decreased in the presence of retinal. The diminution in protein binding due to retinal was not caused by differences in the amount of antibody bound and this was shown by two experiments. First, specific antibody protein binding to liposomes was directly measured and was essentially unaffected by retinal. Second, liposomes were prepared from lipid extracts of sheep erythrocytes. These liposomes were used as as immunoadsorbants to remove antisheep erythrocyte antibodies. The immunoadsorbant capacity was the same in both the presence and the absence of retinal. A further conclusion from these experiments was that retinal did not change the number of liposomal glycolipid antigen molecules available for antibody binding and thus presumably did not change the total number of lipid molecules present on the outer surface of the liposomes. Retinal did have an effect on the geometric structure of the liposomes. Size distribution measurements were performed in the diameter range of 1-6.35 mum by using an electronic particle size analyzer (Coulter Counter). Liposomes containing retinal were shifted toward smaller sizes and had less total surface area and volume. It was suggested that retinal-containing liposomes may have had a tighter packing of the molecules in the phospholipid bilayer. This effect of retinal on liposomal structure may have been responsible for the observed decreased binding of C3 and total complement protein.