CXCR4/IgG-expressing plasma cells are associated with human gastrointestinal tissue inflammation

Abstract

Background: We previously reported abnormalities in circulating B cells in patients with chronic granulomatous disease (CGD) and those with HIV infection. Gastrointestinal complications are common to both diseases and likely involve perturbation of immune cells, including plasma cells (PCs). IgA is the most abundant immunoglobulin in the human body, with roles in protection and maintenance of intestinal homeostasis. IgA is produced primarily by PCs residing in mucosal tissues that are also thought to circulate in the blood.

Objective: We sought to characterize and compare PCs in patients with infectious (HIV) and noninfectious (CGD and Crohn disease) diseases that have been associated with intestinal inflammation.

Methods: Phenotypic and transcriptional analyses were performed on cells isolated from the blood and colon.

Results: IgA-secreting CCR10-expressing PCs predominated in the guts of healthy subjects, whereas in patients with HIV, CGD, and Crohn disease, there was a significant increase in the proportion of IgG-secreting PCs. Where intestinal inflammation was present, IgG-secreting PCs expressed reduced levels of CCR10 and increased levels of CXCR4. The intensity of CXCR4 expression correlated with the frequency of IgG-expressing PCs and the frequency of CXCR4(+)/IgG(+) PCs was associated with the severity of intestinal inflammatory disease yet distinct from PCs and plasmablasts circulating in the blood.

Conclusions: These findings suggest that regardless of the underlying disease, the presence of CXCR4(+)/IgG(+) PCs in the gut is a strong yet localized indicator of intestinal inflammation. Furthermore, our findings suggest that CXCR4(+)/IgG(+) PCs might play a role in immune cell homeostasis during inflammatory processes of the gut.

Keywords: Plasma cells; gastrointestinal inflammation; homing receptors; inflammatory bowel disease; primary and infectious immunodeficiencies.

FIG 1

Identification of gut-derived PCs by using flow cytometry. A, PCs of a representative HD were defined as CD19⁺CD3⁻CD20⁻CD27⁺⁺ within the lymphocyte gate. Each plot title identifies the gated cell population, and numbers indicate cell percentages in each quadrant or gate. FSC, Forward scatter; SSC, side scatter. B, The immunoglobulin isotype profile was determined with 2 separate stains: one for IgA and IgG and the other for IgM and IgD.

FIG 2

Characterization of dual IgA/IgG-expressing PCs in the gut. A, Microscopy of sorted PCs stained for IgA (Alexa Fluor 488, green) and IgG (Alexa Fluor 594, red). Arrows show dual positivity. B, Expression of immunoglobulin light chains for single IgG- or IgA-expressing and dual IgG/IgA-expressing PCs. Numbers indicate cell percentages in each quadrant. The dotted box identifies cells sorted for transcriptional analysis (see Fig E1).

FIG 3

Immunoglobulin isotype distribution among gut-derived and peripheral blood PCs/plasmablasts. A and B, Immunoglobulin isotype mean distribution (Fig 3, A) and median comparisons of gut-derived PCs (Fig 3, B) from the groups described in Table I. Light gray triangles, Patients with CGD with no gastrointestinal symptoms. C and D, Analyses were performed on peripheral blood PCs/plasmablasts from participants in Table I. Horizontal bars represent medians. NS, Not significant.

FIG 4

Expression of CCR10 on gut-derived PCs. A, Representative plots of CCR10 expression by IgA and IgG are shown by group. Numbers indicate cell percentages in each quadrant. B and C, Histograms from plots in Fig 4, A (Fig 4, B), and group comparisons of CCR10 expression (Fig 4, C) were obtained by gating on single IgG- or IgA-expressing and dual IgG/IgA-expressing PCs. Horizontal bars represent medians and asterisks and light gray triangles identify IgA-deficient subjects and patients with CGD with no gastrointestinal symptoms from Table I, respectively. NS, Not significant.

FIG 5

Expression of CXCR4 on gut-derived PCs. Analyses for CXCR4 were identical to those presented for CCR10 in Fig 4.

FIG 6

Correlation and association between CXCR4, IgG, and combined scores. Comparisons were performed between fraction of gut-derived PCs expressing only IgG and the intensity (MFI) of CXCR4 expression on PCs expressing only IgG (A) and the percentage of CXCR4⁺ PCs expressing only IgG and the combined pathology and gastrointestinal symptom scores described in Table I (B).