Human monocyte interaction with antibody-coated platelets. I. General characteristics.

The interaction of human monocytes with antibody-coated and normal platelets was studied using an assay system that employed rate zonal centrifugation to separate monocyte-associated (bound) platelets from free platelets. At a monocyte:platelet ratio of 1:10, monocytes bound 21.2 +/- 6.6% of antibody-coated platelets and less than 2.2 +/- 1.3% of control platelets. Monocyte binding of antibody-coated platelets was rapid and inhibited by monomeric IgG and staphylococcal protein A. Specific binding was positively related to the number of monocytes present and the amount of IgG displayed on the platelet surface. Transmission and scanning electron micrographs illustrate the membrane binding of antibody-coated platelets to monocytes and suggest that phagocytosis of platelet targets occurs as well. Thus, these observations indicate that monocytes can participate in Fc-receptor binding of anti-PlA1-sensitized platelets. This novel assay may be useful in the analysis of monocyte-macrophage Fc-receptor interaction with platelets sensitized with IgG from both iso- and autoimmune disorders as well as in the characterization of treatment modalities which may alter monocyte Fc-receptor recognition and binding.

Selective loss of mitochondrial genome can be caused by certain unsaturated fatty acids.

Various unsaturated fatty acids had different effectiveness for maintaining the continued replication of functional mitochondria in an unsaturated fatty acid auxotroph of Saccharomyces cerevisiae (KD115). Certain isomers of octadecenoic acid (i.e., cis-9) and eicosatrienoic acid (i.e.,cis-8,11,14) permitted continued replication of mitochondria and provided cultures that contained only 4 to 5% cells that formed petite colonies. On the other hand, cultures grown with cis-12- or cis-13-octadecenoic acid or cis-11,14,17-eicosatrienoic acid, produced a 12- to 16-fold greater frequency of petite mutants (50-60%) after 8 to 10 generations of growth. The production of the petite mutants occurred despite adequate incorporation of these unsaturated fatty acids into cellular phospholipids and an apparently normal ability to undergo the initial steps in the induction of cellular respiration. The evidence suggests that some cellular processes necessary for continued mitochondrial replication depend on the structural features of the fatty acyl chains as well as the overall content of unsaturated fatty acids in membrane phospholipids. Impairment of that process by certain inadequate fatty acids or by an inadequate supply of a suitable fatty acid leads to a permanent loss of the mitochondrial genome from the cells of subsequent generations.

Quantitative effects of unsaturated fatty acids in microbial mutants. VII. Influence of the acetylenic bond location on the effectiveness of acyl chains.

The ability of a series of 18 carbon acetylenic fatty acids to fulfill the unsaturated fatty acid requirements of Escherichia coli and Saccharomyces cerevisiae was investigated. Despite their high melting points (greater than 40 degrees C), several isomers of the acetylenic fatty acids were as efficient or more efficient in supporting growth than the analogous fatty acid having a cis-double bond. The efficiencies of the different positional isomers in supporting cell proliferation varied from essentially 0 cells per fmol for the 2-5 and 13-17 isomers to high values when the acetylenic bond was near the center of the chain: e.g. 45 E. coli and 5.5 S. cerevisiae cells/fmol for the 10 isomer. A striking ineffectiveness of the 9 isomer was observed with E. coli. The 7, 8 and 10 isomers were at least 10-fold more efficient than any of the other positional isomers in supporting the growth of E. coli. In contrast, the 9 isomer was among the most effective acetylenic fatty acids tested with the yeast mutant. Chromatographic analysis of the extracted lipids indicated that each of the acetylenic isomers tested (except delta2 and delta3) could be esterified by the prokaryotic and eukaryotic microorganisms. The content of unsaturated plus cyclopropane acids observed when growth ceased in E. coli cultures supplemented with growth-limiting concentrations of the acetylenic fatty acids ranged from approx. 15 mol% for the 8 isomer to approx. 35 mol% for the 14 and 17 isomers. The 8-11 isomers were observed to be esterified predominantly at the two position in phosphatidylethanolamine of E. coli and in phosphatidylcholine of S. cerevisiae.