Differential lateral mobility of IgM and IgG receptors in mouse B lymphocyte membranes

Abstract

Anti-Ig induced redistribution of different Ig subclasses was studied as a function of temperature and correlated with membrane phase transitions as revealed by electron spin resonance spectroscopy. Fluorescein isothiocyanate-coupled anti-IgG2 and anti-IgM antibodies induced patching and capping that proceeded with increasing rates from 20 to 40 (measured at 20 intervals). Characteristic temperatures marked the onset of discontinuities in such rate changes. IgG2-bearing lymphocytes displayed discontinuities at 140, 220, 28', and 360, whereas IgM-bearing lymphocytes displaced discontinuities at 180, 240, 320, and 380. Electron spin resonance spectroscopy studies using the spin label 2,2-dimethyl4-butyl4-pentyl-Noxyloxazolidine, a nitroxide-substituted decane, indicated that these temperatures are a function of hydrocarbon phase separations in the B lymphocyte membrane. With a tlucosaminederivative [2(10-carboxydecyl)2-hexyl4,4-dimethyl-3-oxazolidinyloxyl glucosamidel as a probe restricted to the outer monolayer of the plasma membrane, the temperatures 140 and 28°d enoted the onset and end, respectively, of a fluidizing process in the outer monolayers of IgG2-bearing lymphocytes. Temperatures of 180 and 320 denoted these boundaries in IgMbearing lymphocytes. Inner monolayer transitions are associated with the remaining temperatures. We conclude that membranes of IgM-bearing lymphocytes are less fluid than those of IgG2-bearing lymphocytes. The behavior of fluorochrome-labeled anti-Ig reagents at the surface of splenic B lymphocytes has been described in detail by many investigators (1-4). To date, most studies on the mechanical aspects of surface immunoglobulin (slg) redistribution in response to antibody have examined slg movement primarily as a function of time at a few selected temperatures. We have used an alternate approach-namely, the investigation of membrane surface behavior as a function of temperature over a constant increment of time. This tactic has been successfully exploited by a number of investigators for correlating changes in membrane function with changes in membrane physical state (5-7). Changes in the physical state of membranes with changing temperature can be monitored by measuring the partitioning of electron spin resonance (ESR) spin labels (or fluorescent labels) between the aqueous and the hydrocarbon (i.e., membrane) milieu of a membrane suspension.Arrhenius plots of partitioning ratios of probe in hydrocarbon to probe in water versus 1/K show discontinuities at characteristic temperatures at which changes in state (i.e., melting or freezing) occur. These discontinuities arise because the probes used are more soluble in fluid membrane hydrocarbon than in frozen hydrocarbon. Whereas a pure lipid system undergoes a change in state (frozen -fluid) over a discrete and narrow temperature range, observations on binary lipid systems show that "melting" occurs over a wider range of temperatures. The boundaries of this process, termed lateral phase separation, are defined as "characteris...

Electron spin resonance evidence for vertical asymmetry in animal cell membranes

“…Preliminary studies using 12NS-GA and mouse B lymphocytes (specifically, IgG2 bearing cells) revealed only two characteristic temperatures at approximately 14 and 28 °C. Lymphocytes spin labeled with 5N10 displayed the usual four characteristic temperatures (Krolick et al, 1977). These preliminary results suggest that 12NS-GA is a potentially valuable membrane surface probe for intact cells.…”

A multivalent DNA aptamer specific for the B-cell receptor on human lymphoma and leukemia

“…We predict that the bi-loop structure ( Supplementary Figure S1 ) instead of a stem–loop region in TD05 melts with increasing temperature, yielding a low-affinity structure B at physiological temperatures that cannot compete with the thermal instability, resulting in dissociation of the complex. Moreover, it has been reported that, the lateral angle of the mIgM in the membrane changes with temperature due to changes of the hydrocarbon structure of the membrane of B lymphocytes ( 37 ). As the nature of the aptamer–epitope interaction is nonlinear, the aforementioned changes in both aptamer and the membrane of the lymphocytic cells with temperature might negatively affect the complex, leading to dissociation.…”

Myo1g is an active player in maintaining cell stiffness in B‐lymphocytes

“…These differences between cell spreading on α‐IgM and α‐CD44 may be due to changes in cell stiffness. This is supported by a report in which B‐lymphocytes treated with α‐IgM displayed increased membrane rigidity, driving the recovery of membrane tension [Krolick et al, ; Pasternak and Elson, ]. The absence of defects seen in cell spreading induced via α‐IgM can be explained by the compensatory role played by other class I myosins (such as Myo1c and Myo1e that are also expressed in B‐cells) [Maravillas‐Montero et al, ].…”