Spontaneous secretion of interferon gamma and interleukin 4 by human intraepithelial and lamina propria gut lymphocytes

Abstract

Background: Cytokines secreted by intestinal T lymphocytes probably play a critical role in regulation of the gut associated immune responses.

Aims: To quantify interferon gamma (IFN-gamma) and interleukin 4 (IL-4) secreting cells (SC) among human intraepithelial (IEL) and lamina propria (LPL) lymphocytes from the duodenum and right colon in non-pathological situations and in the absence of in vitro stimulation.

Patients: Duodenal and right colonic biopsy specimens were obtained from patients with no inflammation of the intestinal mucosa.

Methods: Intraepithelial and lamina propria cell suspensions were assayed for numbers of cells spontaneously secreting IFN-gamma and IL-4 by a two site reverse enzyme linked immunospot technique (ELISPOT).

Results: The relatively high proportion of duodenal lymphocytes spontaneously secreting IFN-gamma (IEL 3.6%; LPL 1.9%) and IL-4 (IEL 1.3%; LPL 0.7%) contrasted with the very low numbers of spontaneously IFN-gamma SC and the absence of spontaneously IL-4 SC among peripheral blood mononuclear cells. In the basal state, both IFN-gamma and IL-4 were mainly produced by CD4+ cells. Within the colon, only 0.2% of IEL and LPL secreted IFN-gamma in the basal state, and 0.1% secreted IL-4.

Conclusions: Compared with peripheral lymphocytes substantial proportions of intestinal epithelial and lamina propria lymphocytes spontaneously secrete IFN-gamma and/or IL-4. These cytokines are probably involved in the normal homoeostasis of the human intestinal mucosa. Disturbances in their secretion could play a role in the pathogenesis of gastrointestinal diseases.

Figure 1

Numbers of IFN-γ and/or IL-4 secreting cells per 10⁵ lymphocytes within IEL and LPL cell suspensions obtained from normal human intestinal duodenal and colonic mucosae. Individual results are shown and horizontal bars indicate the medians.

Figure 2

Dot plots from three colour flow cytometric analysis for anti-IFN-γ on CD3⁺ and on CD8⁺ or CD8 cells for IEL and LPL. The cells were cultured for four hours with PMA and ionophore A 23187 in the presence of brefeldin A. The fluorescence plots shown are representative of one of three different experiments and cells analysed were gated for CD3⁺ cells so that results are given as percentage of CD3⁺ cells. Control isotype was used to differentiate positive from negative immunofluorescence.