BLOOD 



These data, together with independent observations by Stroud 

 and Brues (33) on the protective action of injected Fraction III, 

 the fraction into which properdin is concentrated during plasma 

 fractionation, led Pillemer to the cautious suggestion that a lack 

 of properdin is connected with the susceptibility to bacteremia 

 following total body irradiation. It seems clear that the chance 

 discovery of this important substance has already made possible 

 a unified rational approach to several basic and hitherto poorly 

 understood phenomena. 



The primary mechanism for resistance against bacterial 

 invasion depends upon the phagocytic function of the leuko- 

 cytes. Consistent with the active nature of this process, white 

 cells are extremely active metabolically. Isolated white cells 

 require a well-balanced biochemical environment for normal 

 activity (36). Citrate ions and other chelating agents commonly 

 used as anticoagulants are toxic, probably because many of the 

 intracellular enzymes require metal activators. Consistent with 

 this, divalent cations such as calcium and magnesium are essen- 

 tial components of any solution which promotes optimal activity. 

 As might be anticipated, preservation of white cells outside the 

 body is successful only when the cells are effectively freed from 

 other formed elements and from plasma, and are placed in an 

 environment where metabolic and physical activity is minimal. 

 The latter conditions are approached when the temperature is 

 reduced to 4 ° C. and the cells are immobilized in a buffered 

 gelatin gel. After storage under these conditions for a week, 

 approximately 50% of the cells exhibit normal viability char- 

 acteristics when returned to a normal environment and tempera- 

 ture. It was observed, however, that preserved cells would ex- 

 hibit normal phagocytic activity only when fresh serum was 

 added to the medium. Attempts to substitute pure albumin for 

 the serum protein failed; indeed, albumin inhibited the slight 

 residual phagocytic ability of the cells in protein-free media. 

 Following this lead, two discrete fractions have been obtained 

 (37) from plasma; when either is added to the white cell medium, 

 good phagocytic activity is observed. Tentatively called phago- 



665 



