Neutropenia induced by systemic infusion of lactoferrin

Rabbit granulocyte lactoferrin, when infused into hamsters or rabbits, induces transient neutropenia, and in hamsters the lactoferrin promotes adherence of the granulocytes to the endothelial cell wall as monitored visually. In contrast, neither rabbit granule lysozyme nor human transferrin induces neutropenia in the rabbit nor does transferrin or bovine serum albumin affect the adherent properties in vivo of the phagocytic cells of the hamster. Thus lactoferrin enhances granulocyte adherence both in vivo and in vitro. It would appear that the promotion of margination of leukocytes by lactoferrin in vivo may contribute to the phenomenon of neutropenia during activation of granulocytes by chemotactic factors.

Mechanism of dexamethasone inhibition of chemotactic factor induced granulocyte aggregation

The reaction of FMLP with granulocytes causes aggregation and degranulation and enhances adherence to endothelium. To evaluate whether prevention of granule extrusion could impair these granulocyte activities, granulocytes were treated with either dexamethasone or hydrocortisone prior to treatment with FMLP. Dexamethasone was added to suspensions of cytochalasin B-treated granulocytes; it markedly impaired the aggregation response of the granulocytes of FMLP. When cytochalasin-B was not used, granulocyte aggregation in response to FMLP or PMA was inhibited by dexamethasone. Although dexamethasone prevented aggregation of cells following stimulation with FMLP or PMA, it failed to prevent the aggregation of granulocytes induced by rabbit lactoferrin. Adherence of granulocytes to human endothelial monolayers was enhanced by FMLP; dexamethasone inhibited the enhancement. However, with the addition of human lactoferrin to the granulocytes exposed to dexamethasone, the cells were able to adhere as well to endothelium as the cells exposed to FMLP but free of dexamethasone. When cytochalasin-B-treated granulocytes were incubated with dexamethasone or hydrocortisone prior to the addition of FMLP, the subsequent release of lactoferrin was substantially blocked, whereas the release of the primary granule products, lysozyme and beta-glucuronidase, was attenuated but not completely blocked. Thus, corticosteroids might block chemotactic-factor-induced granulocyte aggregation by selectively preventing release of specific granule products that contribute to and sustain aggregation.

Rabbit cationic protein enhances leukocyte adhesiveness

Cationic protein purified from rabbit peritoneal polymorphonuclear leukocytes (PMN) was demonstrated to incite autoaggregation of the rabbit PMN and promote adhesiveness of human PMN to endothelial cells. PMN aggregation induced by supernatants derived from secretory PMN was blocked by a specific anticationic protein antibody. These studies reveal that a positively charged protein derived from the PMN can alter surface properties of the PMN itself and imply a role for this protein in PMN immobilization at inflammatory sites.

Lactoferrin: a promoter of polymorphonuclear leukocyte adhesiveness

Polymorphonuclear leukocytes (PMN) degranulate, adhere to vascular endothelium, or aggregate to each other following exposure of the cells to high concentrations of chemotactic stimuli such as formyl-methionyl-leucyl phenylalanine (FMLP). PMN released the specific granule product lactoferrin more readily in response to chemotactic stimuli, which correlated with promotion of PMN aggregation as measured by light transmission and enhanced PMN adherence. Both concanavalin A (Con-A) and phorbol myristate acetate (PMA), agents that lead to specific granule discharge, induced and sustained human PMN aggregation. Similarly, supernatants, generated from Con-A-treated PMN, aggregated fresh PMN in the presence of alpha-methylmannoside, a competitive inhibitor of the lectin. Anti-human lactoferrin IgG but not normal goat IgG blunted the aggregation elicited by both PMA and FMLP. Both human milk lactoferrin and rabbit PMN lactoferrin aggregated human lactoferrin promoted PMN adherence to endothelial cells. The enhanced PMN stickiness was correlated with the early phase of degranulation. Thus, PMN lactoferrin serves an autoregulatory role to retain PMN at inflammatory sites to amplify the inflammatory response.

Purification of myosin light chain kinase from rabbit polymorphonuclear leukocytes

To investigate the regulation of actin-myosin interaction in rabbit phagocytic cells, purified myosin and a partially purified cofactor protein were obtained from polymorphonuclear leukocytes (PMN) and alveolar macrophages (ALM) by molecular sieve filtration over an agarose column. ALM cofactor enhanced the Mg++-ATPase activity of ALM myosin by actin to 0.15 +/- 0.04 mumoles Pi per mg myosin per min and PMN cofactor enhanced PMN myosin to 0.43 +/- 0.03 mumoles Pi per mg myosin per min. The crude cofactor preparations isolated from the two types of leukocyte extracts were interchangeable with the leukocyte myosins. When ALM cofactor was added to a PMN actomyosin complex, the Mg++-ATPase activity of the PMN myosin was 3-fold higher than with ALM cofactor and its own actomyosin complex. In contrast, PMN cofactor did not enhance ALM actomyosin Mg++-ATPase activity beyond that observed with ALM cofactor and ALM actomyosin. Cofactor protein from the PMN was further purified on a DEAE-Sephagel column. After electrophoresis on sodium dodecyl sulfate-polyacrylamide gel, the isolated fraction weighed 70,000 daltons. This fraction stimulated the actinmediated myosin Mg++-ATPase. In the presence of Mg++ and [gamma 32P]ATP, the 70,000 dalton protein phosphorylated the 20,000 dalton light chain of PMN myosin, leading to the incorporation of 0.62 +/- 0.09 moles of Pi per mole myosin. On the basis of these results, we propose that phagocytic cofactor is a kinase which regulates the enzymatic activity of phagocytic cell myosin.

Reduction of endogenous nucleic acid in a single-cell protein

The reduction of nucleic acid by an endogenous polynucleotide phosphorylase and ribonuclease in cells of Brevibacterium JM98A (ATCC 29895) was studied. A simple process was developed for the activation of the endogenous RNA-degrading enzyme(s). RNA degradation was activated by the presence of Pi with 14.2 mumol of ribonucleoside 5'-monophosphate per g of cell mass accumulating extracellularly. The optimum pH for degradation of RNA was 10.5 and the optimum temperature was 55 to 60 degrees C. Enzymatic activity was inhibited by the presence of Ca2+, Zn2+, or Mg2+. Although some of the RNA-degrading enzymatic activity was associated with the ribosomal fraction, most was soluble. Both polynucleotide phosphorylase and ribonuclease activities were identified.

Enhancement of chemotactic response and microtubule assembly in human leukocytes by ascorbic acid

The incubation of human leukocytes with ascorbic acid increased chemotaxis of the cells. In addition, ascorbic acid promoted the assembly of intracellular polymorphonuclear leukocyte (PMN) with colchicine blocked the effect of ascorbic acid on promoting microtubule assembly. Not only did ascorbic acid promote the assembly of microtubules in vivo, but it enhanced the assembly of bovine brain tubulin into microtubules in vitro as quantitated by a glass-fiber filtration assay and by promotion of viscosity changes. The enhancement in leukocyte mobility by ascorbate at concentrations achievable in normal tissues correlates with its ability to assemble microtubule organelles.

Purification of an Endogenous polynucleotide phosphorylase from Brevibacterium JM98A

Polynucleotide phosphorylase was purified form Brevibacterium JM98A (ATCC 29895). Homopolynucleotides were arsenolysed in the order polyadenylate greater than polycytidylic acid greater than polyuridylic acid greater than polyguanylate. The products were ribonucleoside 5'-monophosphates.