Control of the erythrocyte membrane shape: recovery from the effect of crenating agents.

ABSTRACT Intact erythrocytes become immediately crenated upon addition of 2,4-dinitrophenol (DNP) or pyrenebutyric acid (PBA). However, when cells are incubated at 37 °C in the presence of the crenating agents with glucose, they gradually (4-8 h) recover the normal biconcave disc form. The recovery process does not reflect a gradual inactivation of DNP or PBA since fresh cells are equally crenated by the supernatant from the recovered cells. Further, after recovery and removal of the crenating agents, cells are found to be desensitized to the readdition of DNP as well as to the addition of PBA, but they are more sensitive to cupping by chlorpromazine. This alteration in the cell \membrane responsiveness was reversible upon further incubation in the absence of DNP. Recovery s dependent upon cellular metabolic state since an energy source is needed and incubation with uanosine but not adenosine will accelerate conversion to the disc shape. It is suggested that the conversion of cells from crenated to disc shape in the presence of the crenators, represents an alteration or rearrangement of membrane components rather than a redistribution of the crenators within the membrane. This shape recovery process may be important for erythrocyte shape preservation as well as shape control in other cells. The morphology of eukaryotic cells provides a visual manifestatio

Multicolor Cytoenzymatic Evaluation of Dipeptidyl Peptidase IV (CD26) Function in Normal and Neoplastic Human T-Lymphocyte Populations

Dipeptidyl peptidase IV (DPP IV), also identified as the glycoprotein CD26, is a transmembrane 110- to 120-kDa serine aminopeptidase involved in immune responses by influencing T-cell costimulation and by cleaving cytokines. Additionally, CD26 is a nonintegrin receptor that contains a binding site for extracellular matrix and other molecules. In order to further define the expression and functional activity of this membrane exopeptidase in human T cells, we developed a nondisruptive, four-color cytofluorogenic assay that utilizes three separate antibodies to cell-surface molecules (e.g., CD4/CD8/CD26 and CD19/CD56/CD26) along with a rhodamine 110-conjugated dipeptide substrate that allows the measurement of DPP IV activity in phenotypically defined cells. We found normal human thymi to have notable differences in time-dependent DPP IV activity among the thymocyte subsets defined by their CD4/CD8 phenotype, with CD4(−)/CD8(−) thymocytes containing less DPP IV activity than cells expressing CD4 and/or CD8 (i.e., maturing). CD26 positivity was moderately intense in thymocytes and tended to identify cells with higher DPP IV activity. The four-color technique was also used to examine mature peripheral blood lymphocytes, along with an assortment of leukemias and transformed T-cell lines. These experiments revealed that while DPP IV was consistently evident in normal T cells, neoplastic T cells could vary in their expression patterns. Furthermore, the presence (or intensity) of surface CD26 in some abnormal T cells and certain normal peripheral blood mononuclear cells was separable from the level of DPP IV measured intracellularly. Our results established that multicolor cytofluorographic analysis can be a practical means to measure DPP IV activity in various human cell populations. Furthermore, we found that DPP IV activity could vary in T cells according to their differentiation status and that under certain circumstances surface CD26 expression can be disassociated from the level of measured enzyme (i.e., DPP IV) activity