Acidic pH increases the avidity of FcgammaR for immune complexes.

The interaction of immunoglobulin G (IgG) antibodies with FcgammaR constitutes a critical mechanism through which IgG antibody effector functions are mediated. In the current work we have examined whether human neutrophil FcgammaR exhibit pH dependence in their association with IgG. Binding assays were performed in culture medium adjusted to different pH values. It was found that the binding of either heat-aggregated human IgG (AIgG), soluble immune complexes (sIC) or IgG-coated erythrocytes (IgG-E) was markedly higher at pH 6.5 than at pH 7.3. This effect was not observed when saturation of FcgammaR was achieved, suggesting that acidic pH increases the avidity of FcgammaR for IC without modifying the total binding capacity. Similar results were observed for the binding of AIgG to either monocytes, natural killer (NK) or K562 cells, suggesting that acidic pH increases the avidity of both, FcgammaRII and FcgammaRIII. Additional experiments were performed to analyse whether the binding of IgG to FcgammaRI also showed pH dependence. To this aim, we employed interferon-gamma-treated human neutrophils and mouse inflammatory macrophages, previously incubated with blocking antibodies directed to FcgammaRII and FcgammaRIII. Acidic pH did not enhance the binding of AIgG nor monomeric IgG under these experimental conditions. Further studies are required to determine whether the enhancement of FcgammaR avidity for IC could be attributed to titration of histidine(s) residues on the Fc fragment of IgG.

Extracellular acidification induces human neutrophil activation.

In the current work, we evaluated the effect of extracellular acidification on neutrophil physiology. Neutrophils suspended in bicarbonate-buffered RPMI 1640 medium adjusted to acidic pH values (pH 6.5-7.0) underwent: 1) a rapid transient increase in intracellular free calcium concentration levels; 2) an increase in the forward light scattering properties; and 3) the up-regulation of surface expression of CD18. By contrast, extracellular acidosis was unable to induce neither the production of H2O2 nor the release of myeloperoxidase. Acidic extracellular pH also modulated the functional profile of neutrophils in response to conventional agonists such as FMLP, precipiting immune complexes, and opsonized zymosan. It was found that not only calcium mobilization, shape change response, and up-regulation of CD18 expression but also production of H2O2 and release of myeloperoxidase were markedly enhanced in neutrophils stimulated in acidic pH medium. Moreover, extracellular acidosis significantly delayed neutrophil apoptosis and concomitantly extended neutrophil functional lifespan. Extracellular acidification induced an immediate and abrupt fall in the intracellular pH, which persisted over the 240-s analyzed. A similar abrupt drop in the intracellular pH was detected in cells suspended in bicarbonate-supplemented PBS but not in those suspended in bicarbonate-free PBS. A role for intracellular acidification in neutrophil activation is suggested by the fact that only neutrophils suspended in bicarbonate-buffered media (i.e., RPMI 1640 and bicarbonate-supplemented PBS) underwent significant shape changes in response to extracellular acidification. Together, our results support the notion that extracellular acidosis may intensify acute inflammatory responses by inducing neutrophil activation as well as by delaying spontaneous apoptosis and extending neutrophil functional lifespan.

Losartan, a selective inhibitor of subtype AT1 receptors for angiotensin II, inhibits the binding of N-formylmethionyl-leucyl-phenylalanine to neutrophil receptors.

Losartan, a selective antagonist of AT1 receptors for angiotensin II, is widely used clinically to manage hypertension. We report here that losartan markedly inhibits neutrophil shape change, adherence and chemiluminescence responses triggered by N-formylmethionyl-leucyl-phenylalanine (fMLP), without affecting responses induced by immune complexes, zymosan or concanavalin A. Neither saralasin, another antagonist of angiotensin II receptors, nor captopril, an angiotensin-converting enzyme inhibitor, reproduced the effects of losartan. It was also observed that neutrophil responses triggered by fMLP were not affected by exogenously added angiotensin II. The effect of losartan on the binding of fMLP was measured using [3H]fMLP. It was found that losartan inhibits the binding of [3H]fMLP to neutrophil receptors. As observed for neutrophils, studies performed with monocytes showed that losartan inhibits chemiluminescence emission triggered by fMLP, without affecting chemiluminescence responses triggered by immune complexes, zymosan or concanavalin A.

Inhibition of human neutrophil apoptosis by platelets.

In the absence of appropriate stimuli, polymorphonuclear neutrophils rapidly undergo characteristic changes indicative of programmed cell death or apoptosis. We report here that neutrophils cultured in the presence of platelets (neutrophil:platelet ratios of 1:50, 1:25, and 1:10) show a dramatic inhibition of apoptosis compared with neutrophils cultured alone. Similar degrees of apoptosis delay were induced by viable unstimulated platelets, fixed unstimulated platelets, or fixed activated (1 U/ml thrombin) platelets. Inhibition of apoptosis was associated with prolongation of the functional lifespan of the neutrophil, as indicated by the higher capacity of platelet-treated neutrophils to display chemiluminescence responses triggered by FMLP, immune complexes, and zymosan. The mechanism responsible for the inhibition of neutrophil apoptosis by platelets has not yet been defined. However, it seems that classical recognition systems such as those mediated by the interaction between platelet P-selectin (CD62) or glycoprotein IIb/IIIa complex and their counter-receptors expressed by neutrophils are not involved.

Activation of human neutrophils and monocytes induced by immune complexes prepared with cationized antibodies or antigens.

We have recently showed that soluble immune complexes (IC) prepared with cationic antibodies (catIC) induce high levels of neutrophil-mediated cytotoxicity against nonsensitized target cells. In the present work we extended our previous findings by studying the ability of catIC to induce different responses mediated by monocytes and/or neutrophils: monocyte cytotoxicity against nonsensitized target cells, chemiluminescence emission by monocytes and neutrophils, and elastase release from neutrophils. Our results showed that, in all cases, cell responses induced by catIC were markedly higher than those induced by control IC, indicating that cationized antibodies enhance IC ability to trigger phagocytic cell activation. A second aim of the present study was to analyze the effect of antigen cationization on IC properties. Interestingly, we found that all the phagocytic cell responses induced by IC prepared with cationized ovalbumin (OA) were significantly higher than those induced by IC prepared with untreated OA. Our results suggest that the charge of antibody and/or antigen constitutes a critical property that conditions the biological activity of IC. Furthermore, these findings support an important role of cationic antibodies and antigens in the development of inflammatory events associated with certain IC-induced diseases.

Afasia anómica como expresión de un status de crisis parciales / Anomic aphasia and partial seizure status

Se presenta una afasia anómica o amnésica que se inició en forma paroxística acompañada de sacudidas clónicas en miembro superior derecho. La paciente diestra, de 59 años tenía antecedentes de convulsiones generalizadas como secuela de un infarto cerebral hipertensivo. Recibía dosis adecuadas de difenilhidantoína (PHT) desde dos años antes al debutar sus primeras crisis. Un pattern de status eléctrico mostró el electroencefalograma inicial, con puntas y polipuntas repetitivas sobre el temporal izquierdo. Se extendían hacia ambos hemisferios, constituyendo muy frecuentes paroxismos generalizados de corta duración. Aunque desaparecieron los clónicas focales del miembro superior derecho con el incremento de la dosis de PHT a 400 mg/día, la afasia anómica no sufrió modificaciones. Su lenguaje oral y escrito se caracterizaba por latencias y perífrasis ante las denominaciones, sin parafasias. Nunca estuvo disártrica y la comprensión era totalmente normal. Durante toda la evolución de su disfasia se mantuvo apática e indiferente con disminución de su espontaneidad, aunque sin anosognosia de su déficit. Se obtuvo una rápida y significativa mejoría, tanto clínica como electrofisiológica, al iniciarse carbamazepina en forma oral. Son de interés los hallazcos asociados, la evolución y exámenes complementarios. En este caso interesa resaltar lo escasamente frecuente de este cuadro clínico como expresión de un status parcial prolongado, la diferente evolución ante distintas drogas y la importancia de los estudios neurofisiológicos y su monitoreo

Afasia anómica como expresión de un status de crisis parciales / Anomic aphasia and partial seizure status

Se presenta una afasia anómica o amnésica que se inició en forma paroxística acompañada de sacudidas clónicas en miembro superior derecho. La paciente diestra, de 59 años tenía antecedentes de convulsiones generalizadas como secuela de un infarto cerebral hipertensivo. Recibía dosis adecuadas de difenilhidantoína (PHT) desde dos años antes al debutar sus primeras crisis. Un pattern de status eléctrico mostró el electroencefalograma inicial, con puntas y polipuntas repetitivas sobre el temporal izquierdo. Se extendían hacia ambos hemisferios, constituyendo muy frecuentes paroxismos generalizados de corta duración. Aunque desaparecieron los clónicas focales del miembro superior derecho con el incremento de la dosis de PHT a 400 mg/día, la afasia anómica no sufrió modificaciones. Su lenguaje oral y escrito se caracterizaba por latencias y perífrasis ante las denominaciones, sin parafasias. Nunca estuvo disártrica y la comprensión era totalmente normal. Durante toda la evolución de su disfasia se mantuvo apática e indiferente con disminución de su espontaneidad, aunque sin anosognosia de su déficit. Se obtuvo una rápida y significativa mejoría, tanto clínica como electrofisiológica, al iniciarse carbamazepina en forma oral. Son de interés los hallazcos asociados, la evolución y exámenes complementarios. En este caso interesa resaltar lo escasamente frecuente de este cuadro clínico como expresión de un status parcial prolongado, la diferente evolución ante distintas drogas y la importancia de los estudios neurofisiológicos y su monitoreo