Peter R.B. Caldwell

Angiotensin-converting enzyme: Effect of antienzyme antibody in vivo

Angiotensin-converting enzyme (EC 3.4.15.1) is a mammalian COOH-terminal dipeptidyl peptidase which catalyzes the release of His-Leu from angiotensin I to yield angiotensin II [ 11, the vasoactive agent of the renin-angiotensin system [2]. The same enzyme inactivates bradykinin, a vasodepressor nonapeptide, by cleavage of the COOH-terminal and adjacent dipeptides [3,4]. We have recently shown, using specific fluorescein-labeled antibody, that converting enzyme is present in the luminal cells of the vasculature of every organ examined, including lung, liver, kidney, pancreas, adrenal and spleen [5]. While extrapulmonary conversion [6-91 and converting activity [lO,l l] are well documented, the lung is thought to play an important role in both conversion of angiotensin I to II [ 12,131 and the degradation of bradykinin [ 141 in the circulation. This is because the lung is perfused by the entire circulating blood volume and has a very large capillary surface area. Further, enzymatically generated angiotensin II is not taken up by the lung [ 13,151 but delivered to the systemic circulation where it exerts its pressor effect. Recent immunohistochemical evidence has indicated that pulmonary converting enzyme may be localized on the luminal surface of the endothelial cells [ 161. The possibility that converting enzyme is accessible to circulating antibodies prompted us to examine the effects in vivo of antibody with anticatalytic activity.

Cellular mechanisms of adaptation of grafts to antibody

New, more effective, strategies of immunosuppression, including those recently designed to induce durable T cell tolerance (by grafting allogeneic or xenogeneic haematopoietic cells into T lymphocyte-depleted recipients), leave humoral rejection as the main barrier to transplantation of vascularized organs between different species. Recent experimental work indicates that hyperacute rejection can be prevented by manipulations of antibodies and complement. In this paper, we review the mechanisms governing the interaction of antibodies with cell surface antigens in vitro and in vivo, and their cellular consequences. Evidence is presented that, in appropriate conditions, antibodies can protect by effecting modification of graft antigenicity (adaptation or accommodation).

The binding of 2,3-diphosphoglycerate as a conformational probe of human hemoglobins

Abstract Since 2,3-diphosphoglyeerate preferentially binds to deoxygenated hemoglobin A, this binding reaction can be used to detect the change in quaternary conformation of hemoglobin associated with the change in ligand state of the hemes. We have studied the binding to two M hemoglobins (MHydePark, MMilwaukee-1) that have the substituted chains in the ferric state, as well as to the mixed liganded hybrids α∗2β2 and α2β∗2 (∗ heme in cyanmet form) prepared from hemoglobins A and H. The studies demonstrate that when these hemoglobin variants and derivatives are deoxygenated, they bind the organic phosphate to an extent similar, but not identical, to that for fully deoxygenated hemoglobin A. The results indicate that removal of ligand from only two of the four hemes results in a change in quaternary structure to a deoxy-like conformation.

In vivo interaction of antibodies with cell surface proteins used as antigens.

Antibody interactions with cell membrane glycoproteins in vivo exhibit features of aggregation and capping with resultant shedding similar to those events described in several in vitro isolated cell systems. Requirements for divalent ligand binding and participation of cytoskeletal elements are demonstrated in vivo as well. Persistence of antigen in immune complexes with complement interaction in situ appear to be necessary to induce an inflammatory response in vivo. Abrogation of this response occurs when circumstances permit antigenic modulation with disappearance of the immune complex.

Biological and biochemical properties of angiotensin-converting enzyme.

ConclusionsAngiotensin-converting enzyme catalyzes cleavage of dipeptides from the COOH-termini of a large number of oligopeptides. It is a glycoprotein with a molecular weight of approximately 130,000 to 140,000 and contains a single, large polypeptide chain and one molar equivalent of bound zinc. It is located in blood vessel walls of many organs and is probably exposed on the luminal surface. It is also present in blood and certain parenchymal cells. Its two currently recognized important substrates are angiotensin I and bradykinin, and its action on each may be viewed as vasopressor. Thus, it catalyzes the formation of angiotensin II, a potent vasopressor agent, and the inactivation of bradykinin, a powerful vasodepressor molecule. The lung is important in regulating the level of angiotensin II in the systemic arterial circulation due to its strategic location, its large vascular bed and the fact that enzymatically generated angiotensin II is minimally metabolized in the pulmonary circulation. Studies with venom peptide inhibitors suggest that the enzyme may represent an important therapeutic target in renin-dependent hypertension. The enzyme is apparently accessible to exogenous anticatalytic antibody so that immunologic regulation of its activity may ultimately be feasible in vivo.

Lung injury in rabbits induced by intravenous administration of heterologous polyclonal antibodies to angiotensin converting enzyme (Kininase II)

Antibody interactions with the endothelial cell membrane glycoprotein angiotensin converting enzyme (Kininase II) in vivo exhibit features of aggregation and capping with resultant shedding similar to those events described in several in vitro isolated cell systems. Requirements for divalent ligand binding, deposition of complement and participation of cytoskeletal elements are demonstrated in vivo. Persistence of antigen in immune complexes with complement interaction appear to be necessary to induce an inflammatory response. Abrogation of this response occurs when circumstances permit antigenic modulation with removal of the immune complex from the endothelial surface.

The Influence of pH and Oxygen on the Erythrocyte Content of 2,3-Diphosphoglycerate

In 1917 Hasselbalch first demonstrated a displacement of the oxygen dissociation curve in the blood of patients with disease (HASSELBALCH [1917]), thus challenging the concept that the oxygen equilibrium of blood was constant for any given conditions of temperature and pH. Ten years later Richards and Strauss showed a rightward shift of the oxygen dissociation curve in patients with anemia (RICHARDS and STRAUSS [1927]), but could not identify the cause for the abnormality. During the next decade, studies at altitude by Dill and coworkers (DILL et al. [1931]) and Keys, Hall, and Guzman [1936] showed the same abnormality in acclimatized normal man, suggesting that the alteration might be an adaptive mechanism related to oxygen transport by the blood. In 1938 Keys and Snell demonstrated the displacement in patients with liver disease and proposed that there might be a reduction in the affinity of hemoglobin for oxygen to account for it (KEYS and SNELL [1938]).