Cytokine priming of human basophils: description of allergen 'nonreleasers'.

Interleukins 3 and 5 and GM-CSF enhance histamine release from basophils triggered by various stimuli. In this report, we describe a subset of allergic patients whose basophils release histamine in response to allergen only when primed with cytokine. In the absence of cytokine, there is no detectable response to allergen. These patients, who represent 4-13% of the allergic population, cannot be distinguished by skin test reactivity or severity of allergic symptoms. Allergen nonreleasers tend to have lower titers of allergen-specific IgE than the majority of atopic subjects, but this difference is not significant (average titer of 29.8 for nonreleasers vs. 188 for typical allergies; p = 0.15). They release histamine normally with anti-IgE and with fMLP, indicating that basophils are responsive to signalling through the IgE receptor, and there is no intrinsic defect in degranulation. Thus, in these patients, the IgE-mediated release of inflammatory mediators from basophils is dependent on, rather than merely enhanced by, T cell cytokines. The relationship between these patients and the previously described anti-IgE 'nonreleasers' is discussed.

Radiation-induced apoptosis is differentially regulated in primary B cells from normal mice and mice with the CBA/N X-linked immunodeficiency.

Normal B cells responsive to thymus independent-type 1 Ags (TI-1) are resistant to low doses of ionizing radiation in vivo (200-300 cGy), compared with TI-1 responsive B cells of mice with the CBA/N X-linked immunodeficiency (xid). This difference in radiosensitivity is an intrinsic B cell property; normal B cells adoptively transferred into xid mice remain TI-1-responsive after irradiation in situ. Because irradiation induces programmed cell death (PCD) in lymphocytes, we determined whether PCD were regulated differently in normal and xid B cells. B cells isolated immediately after irradiation from normal or xid donors when cultured without stimulators became apoptotic with the same kinetics and to the same extent, showing that apoptosis was induced equally in both populations. Apoptosis could be suppressed and mitogenesis could be induced frequently, however, if irradiated B cells were cultured with B cell activators. When activators using separate signal transduction pathways were compared, a hierarchy of efficiency at effecting apoptosis rescue was observed, and activators used singly without effect could synergize to protect. xid B cells were more resistant to rescue than normal B cells unless PMA was used as a stimulant. Although the mechanism of activator-induced rescue was not established, selective overexpression of a bcl-2 transgene rendered xid B cells radioresistant. The data suggest that a signal(s) delivered to irradiated B cells in the in vivo microenvironment suppresses apoptosis and that xid B cells and a radiosensitive subpopulation of normal B cells are refractory to this signal(s).

Potential therapeutic recombinant proteins comprised of peptides containing recombined T cell epitopes.

The complete primary structure of Fel d I2 has been determined and shown to be comprised of two separate polypeptide chains (designated chain 1 and 2). Overlapping peptides covering the entire sequence of both chains of Fel d I have been used to map the major areas of human T cell reactivity. The present study describes three non-contiguous T cell reactive regions of < 30 aa in length that were assembled in all six possible configurations using PCR and recombinant DNA methods. These six recombinant proteins comprised of defined non-contiguous T cell epitope regions artificially combined into single polypeptide chains have been expressed in E. coli, highly purified, and examined for their ability to bind to human cat-allergic IgE and for human T cell reactivity. Several of these recombined T cell epitope-containing polypeptides exhibit markedly reduced IgE binding as compared to the native Fel d I. Importantly, the human T cell reactivity to individual T cell epitope-containing regions is maintained even though each was placed in an unnatural position as compared to the native molecule. In addition, T cell responses to potential junctional epitopes were not detected. It was also demonstrated in mice that s.c. injection of T cell epitope-containing polypeptides inhibits the T cell response to the individual peptides upon subsequent challenge in vitro. Thus, these recombined T cell epitope-containing polypeptides, which harbor multiple T cell reactive regions but have significantly reduced reactivity with allergic human IgE, constitute a novel potential approach for desensitization to important allergens.

Differential radiosensitivity among B cell subpopulations.

We have previously shown that low doses of ionizing radiation selectively impair a functionally defined B cell subpopulation. Normal mice, after exposure to 200 rad of ionizing radiation, have normal or near normal splenic plaque-forming cell responses to thymus-independent type 1 Ag, but reduced responses to thymus-independent type 2 Ag. Here, we confirm and extend the original findings by using hapten-specific serum RIA to demonstrate this differential radiosensitivity is systemic. We also examined splenocytes stained with a panel of lymphocyte surface Ag by FACS analysis to determine if these functional changes are accompanied by a physical alteration of the B cell pool of irradiated mice. Single-parameter FACS analyses demonstrate a diminution in both B cell number and the heterogeneity of membrane Ag expression within the surviving B cell pool after irradiation. In contrast, T cells are relatively radioresistant as the relative percentage of T cells in the irradiated splenocyte pool increases, whereas the heterogeneity of membrane Ag expression remains constant. Multiparameter FACS analyses indicate that B cells with the sIgM much greater than sIgD phenotype are more radiosensitive than B cells of the sIgM much less than sIgD phenotype. In addition, immunohistochemical analysis of splenic sections stained with anti-IgM or anti-IgD reveal the enhanced radiosensitivity of marginal zone B cells.