Complement receptors regulate lipopolysaccharide-induced T-cell stimulation

Abstract

Complement receptors type 1 and 2 (CR1 (CD35)/CR2 (CD21)) are known to enhance the adaptive immune response. In mice, CR1/CR2 are expressed on B cells, follicular dendritic cells, and activated granulocytes. Recently, we showed that a subset of CD44high and CD62Llow T cells also expresses CR1 and CR2. We now report that CR1/CR2 are detectable on both CD4+ and CD8+ subsets of T cells. Lipopolysaccharide (LPS) from Gram-negative bacteria causes polyclonal activation of B cells and stimulation of macrophages and other antigen-presenting cells. We further demonstrate that LPS induced marked up-regulation of CD25 and CD69 on T cells from CR1/CR2 sufficient (Cr+/+), but significantly lower up-regulation on T cells from CR1/CR2 deficient (Cr-/-) mice. These findings point to a novel mechanism by which CR1/CR2 modulates the activation of T cells by LPS.

Figure 1

Expression of CR1/CR2 on a subset of CD4⁺ and CD8⁺ T cells. Triple staining of splenocytes from Cr^+/+ mice was performed using PE-labelled anti-CD3, FITC-labelled anti-CR1/CR2, and cytochrome-labelled anti-CD4 or anti-CD8. Numbers present the percentage of CD3⁺, CD4⁺ or CD8⁺ cells staining with the indicated marker Density plot.

Figure 2

Expression of CD69 on Cr^+/+ or CR^–/– T cells. Splenocytes from immunized Cr^+/+ and Cr^–/– mice were cultured in the presence of 25 µg/ml LPS, plate-bound anti-CD3 antibodies, or medium alone for 24 hr followed by FACScan analysis for the expression of CD69 on T cells. Numbers present the percentage of CD3⁺ cells staining with the indicated marker Dotplot. *P < 0·05.

Figure 3

Expression of CD25 and CD69 on CD3⁺ T cells. Splenocytes from immunized wild type mice were cultured in the presence of 10 µg/ml, 25 µg/ml or 100 µg/ml LPS or no antibody (medium), 100 µg/ml control antibody or 100 µg/ml 7G6 mAb for 24 hr followed by FACScan analysis for the expression of CD25 and CD69 on T cells. Numbers present the percentage of CD3⁺ cells staining with the indicated marker. *P < 0·05.

Figure 4

Expression of CD69 and CD25 on T cells in culture with macrophages. Numbers present the percentage of CD3⁺ cells staining with the indicated marker; T, T cells; Mac, macrophages. *P < 0·05.