Plasma cell toll-like receptor (TLR) expression differs from that of B cells, and plasma cell TLR triggering enhances immunoglobulin production

Abstract

Toll-like receptors (TLRs) are key receptors of the innate immune system and show cell subset-specific expression. We investigated the messenger RNA (mRNA) expression of TLR genes in human haematopoietic stem cells (HSC), in naïve B cells, in memory B cells, in plasma cells from palatine tonsils and in plasma cells from peripheral blood. HSC and plasma cells showed unrestricted expression of TLR1-TLR9, in contrast to B cells which lacked TLR3, TLR4 and TLR8 but expressed mRNA of all other TLRs. We demonstrated, for the first time, that TLR triggering of terminally differentiated plasma cells augments immunoglobulin production. Thus, boosting the immediate antibody response by plasma cells upon pathogen recognition may point to a novel role of TLRs.

Figure 1

Messenger RNA (mRNA) expression levels of toll-like receptor (TLR)1–TLR10 show distinct regulation patterns during B-cell development. mRNA expression profiling is shown of TLR1–TLR10 in haematopoietic stem cells (HSC) isolated from cord blood, in naïve B cells, in memory B cells, in terminally differentiated plasma cells from tonsils and in terminally differentiated plasma cells from peripheral blood. HSC and plasma cells were isolated by positive selection using CD34 microbeads and CD138 microbeads, respectively. Naïve B cells and memory B cells were isolated using the naïve B-cell isolation kit and a combination of the B-cell isolation kit II and CD27 microbeads, respectively. Expression of TLR1–TLR10 and of the housekeeping gene hydroxymethylbilane-synthase (HMBS) mRNA was monitored by quantitative real-time polymerase chain reaction (PCR). Results shown are the means ± standard deviation (SD) of three biological replicates of one out of three representative experiments. *Denotes not detectable.

Figure 2

Triggering of toll-like receptors (TLRs) on plasma cells isolated from tonsils induces increased production of immunoglobulin. Intracellular (a) IgM and (b) IgG expression in plasma cells, mean fluorescence intensity of (c) IgM and (d) IgG in plasma cells and (e) secretion of immunoglobulin by plasma cells isolated from tonsils. Plasma cells were isolated from palatine tonsils by positive selection using CD138 microbeads. The viability of plasma cells after 72 hr in culture was always above 75%. Black histograms indicate isotype-control staining. The results shown are the means ± standard deviation of three biological replicates of one out of three representative experiments. *P< 0·001; **P< 0·01; ***P< 0·05, by Kruskall–Wallis and Dunn’s multicomparison test. CpG ODN, cytosine–phosphate–guanosine oligonucleotide 2006; LPS, lipopolysaccharide.

Figure 3

Triggering of toll-like receptors (TLRs) on plasma cells isolated from peripheral blood induces increased production of immunoglobulin. Intracellular (a) IgM and (b) IgG expression, and mean fluorescence intensity of (c) IgM and (d) IgG, in plasma cells isolated from peripheral blood. Plasma cells were isolated from peripheral blood by positive selection using CD138 microbeads. The viability of plasma cells after 72 hr in culture was always above 75%. Black histograms indicate isotype-control staining. The results shown are the means ± standard deviation of three biological replicates of one out of three representative experiments. **P< 0·01, by Kruskall–Wallis and Dunn’s multicomparison test. CpG ODN, cytosine–phosphate–guanosine oligonucleotide 2006; LPS, lipopolysaccharide.