Differential expression of CD32 isoforms following alloactivation of human T cells

Abstract

SUMMARYReceptors for the Fc region of immunoglobulin G ( IgG) (FccRs) exist in three main forms: membrane bound, soluble and cytoplasmic. The function of cytoplasmic FccRs is poorly understood. We have previously demonstrated cytoplasmic FccRII (cCD32) within most normal human peripheral blood lymphocytes (PBL), including T cells. In this study we have investigated the hypothesis that following lymphocyte activation, up-regulation of cCD32 occurs, resulting in increased expression at the cell surface. Normal PBL were activated in vitro using a two-way mixed lymphocyte reaction ( MLR) and expression of CD32 monitored by flow cytometry and by immunoperoxidase staining using specific monoclonal antibodies and aggregated mouse IgG subclasses. Furthermore, we designed oligonucleotide probes specific for the three main isoforms of CD32 and looked for changes in mRNA expression throughout the MLR using an in situ hybridization technique. Increased surface expression of CD32 was found on both activated human T and B lymphocytes, but this was found only in the early stages of the MLR, on days 3 and 4, and was virtually absent by day 7. An inverse relationship between cell surface expression of CD32 and mRNA for the IIb isoforms was noted with strong mRNA expression for IIb isoforms occurring in the later stages of the MLR (days 6-7) when interleukin-2R ( IL-2R)-positive T cells were predominant. A soluble IgG binding factor (soluble CD32?) was also detected in the MLR culture supernatant. These observations provide support for the hypothesis that synthesis of IIb isoforms of CD32 occurs following alloantigen activation of human T lymphocytes.

B‐cell antigens within normal and activated human T cells

“…These observations are therefore consistent with the hypothesis that up‐regulation of these inappropriately expressed CD antigens occurs following T‐cell activation and that these molecules may be actively synthesized and released into the fluid‐phase as soluble immunoregulatory molecules 11 …”

“…Cell‐free supernatants obtained from day 7 MLR‐activated cells contained a soluble IgG binding factor (possibly soluble CD32). Furthermore, mRNA for CD32 (FcγRIIb1 and b2 isoforms) was also demonstrated by in situ hybridization within the cytoplasm of activated PBL, gradually increasing in staining intensity throughout the MLR 11 …”

“…Following cell activation, in a two‐way 7‐day mixed lymphocyte reaction (MLR), expression of CD32 was found at the cell surface but only on days 3–4. By day 7 of the MLR, cell surface expression was lost 11 . Cell‐free supernatants obtained from day 7 MLR‐activated cells contained a soluble IgG binding factor (possibly soluble CD32).…”

Phenotypic differences between healthy effector CTL and leukemic LGL cells support the notion of antigen-triggered clonal transformation in T-LGL leukemia

“…High levels of activating CD32a were consistently found in LGL patients. Ligation of this receptor results in T cell stimulation and enhanced cytokine secretion [68,69]. LGL clones, this feature appears to be much more pronounced.…”

A Simple Immunomonitoring Procedure for mRNA-Loaded Dendritic Cell Therapy

“…This was due to the increased nonspecific background that occurred due to the reactivity with an irrelevant IgG (isotype control). When CD3+ cells were gated before analysis of IFN-␥ -producing cells, this nonspecific binding of isotype control might have been caused by the expression of CD32 (Fc ␥ RII) on activated T cells [16] . Although a similar phenomenon was more remarkably ob- served after 1 week of coculture, we were able to detect IFN-␥ -producing CD8+ T cells when purified CD8+ cells were used for the assay ( fig.…”