Lactoferrin: its role as a Ga-67-binding protein in polymorphonuclear leukocytes.

Gallium-67 bound to lactoferrin--an iron-binding protein found in high concentration in polymorphonuclear leukocytes--has been isolated from PMNs that have previously been incubated with Ga-67 citrate. Although the cell-labeling efficiency was highly variable (0.026-10%), much of the activity that did bind to the PNMs (74.8 +/- 10%) was recovered in the supernatant after sonication and centrifugation. About half (approximately 47%) of the PMN-bound activity was retained after dialysis and was presumably bound to macromolecules in the supernatant. When this retained activity was placed on a column containing immobilized antilactoferrin antibody, almost three quarters of the activity was bound to the column. This bound activity was (36 +/- 17%) of the total activity absorbed by the PMN. The addition to the antilactoferrin column of a known antigen-antibody-dissociating agent caused the disolution of the complex. No significant activity was bound to a control column. The findings indicate that lactoferrin is a major Ga-67-binding protein present in PMNs and suggest that it may play a major role in Ga-67 localization in an abscess. These results support the contention that molecules binding ferric iron have an important effect on Ga-67 distribution in vivo.