Crosstalk between innate and adaptive immune responses to infectious bronchitis virus after vaccination and challenge of chickens varying in serum mannose-binding lectin concentrations

Abstract

Mannose-binding lectin (MBL), a C-type collectin with structural similarities to C1q, is an innate pattern-recognition molecule that is sequestered to sites of inflammation and infections. MBL selectively binds distinct chemical patterns, including carbohydrates expressed on all kinds of pathogens. The present study shows that serum MBL levels influence the ability of chickens to clear the respiratory tract of virus genomes after an infectious bronchitis virus (IBV) infection. The primary IBV infection induced changes in circulating T-cell populations and in the specific antibody responses. Serum MBL levels also influenced IBV vaccine-induced changes in circulating T-cell populations. Moreover, addition of mannose to an IBV vaccine altered both vaccine-induced changes in circulating T-cell populations and IBV specific vaccine and infection-induced antibody responses in chickens with high serum MBL levels. These data demonstrate that MBL is involved in the regulation of the adaptive immune response to IBV.

Fig. 1

Reverse transcriptase-polymerase chain reaction (RT-PCR) profiles of IBV genomes detected in oropharyngeal airway swab samples. The IBV genomes were visualized by ethidium-bromide-stained 1.5% agarose gels. (A) The first and last samples in each row are the positive M41 control except for the last two rows where the M41 control is missing at the right side. The first three rows show samples post vaccination (PV) with a series of 8 samples from the days indicated. The last five rows show samples post infection (PI) with a series of 12 samples from the day indicated. (B) The relative percentage density of virus load in oropharyngeal airway swab samples collected PV and PI. H or L indicates the sub-lines with high or low serum concentration of MBL, respectively; 1, 2 or 3 indicates the treatment groups ‘−vaccination − mannose’ (1), ‘+vaccination − mannose’ (2), and ‘+vaccination + mannose’ (3).

Fig. 2

The MBL serum concentration in L and H-chickens from day 0 to day 28 post vaccination (PV) with live attenuated IBV strain Ma5 vaccine and from day 1 post infection (PI) to day 35 PI with live IBV strain M41. The upper panel shows group 1, the middle panel group 2, and the lower panel group 3. Results are shown as mean values (n = 8) ± SE.

Fig. 3

The specific IBV antibody titer in L and H-chickens measured from days 0 to 28 post vaccination (PV) with live attenuated IBV strain Ma5 vaccine and from days 7 to 35 post infection (PI) with live IBV strain M41. The upper panel shows group 1, the middle panel group 2, and the lower panel group 3. Results are shown as mean values (n = 8) ± SE. Statistically significant differences between H and L-chickens are shown by stars. *Indicates p < 0.05 and **indicates p < 0.01.

Fig. 4

Whole blood flow cytometry. (A) A flow diagram showing the gating strategy. First, small lymphocytes were gated on FCS/SSC dot plots, then CD45^high (lymphocytes) were identified, followed by gating on CD3 positive cells. The CD3 positive cells were finally divided into CD4 or CD8 positive cells. (B) The CD8α+ percentage of CD3+ cells in the left column, the CD4+ percentage plus the CD4+CD8α+ percentage of CD3+ cells in the middle column, and the percentage of the CD4−CD8α− percentage of CD3+ cells is shown to the right. The upper panels show group 1, the middle panels group 2, and the lower panels group 3. Results are shown as mean values (n = 8) ± SE. Statistically significant differences between H and L-chickens are shown by stars. *Indicates p < 0.05 and **indicates p < 0.01.