Porcine non-conventional B-1-like cells are a potent source of -binding IgM.

INTRODUCTION

serotype () 2 is an important bacterial pathogen in piglet nurseries and an emerging zoonotic agent without effective vaccines available. Immunoglobulin (Ig)M plays an essential role in host defense against . In mice, non-conventional B-1 cells are a major source of protective IgM against encapsulated bacterial pathogens, such as . Two IgMCD21 B-1-like cell subpopulations, distinguishable by CD11R1 expression, were described in pigs, but their properties and functions are poorly understood. This study aimed at a first characterization of the porcine early IgM B cell response against 2.

METHODS

We analyzed the same healthy pigs, naturally colonized by different serotypes, including 2, at four and eight weeks of age serologically and determined the frequency of different peripheral B cell subpopulations by flow cytometry. Furthermore, we isolated conventional IgMCD21 B-2 cells as well as non-conventional B-1-like cell subpopulations from peripheral blood of eight-weeks-old pigs to evaluate their potential of IgM secretion in response to innate and adaptive stimuli .

RESULTS

Between the fourth and eighth week of life, a characteristic increase of 2-binding serum IgM antibodies, restricting bacterial growth, was observed. Moreover, we show for the first time that the significant increase of anti- serum IgM is associated with a relative increase of peripheral non-conventional IgMCD21 B-1-like cells , particularly of the IgMCD21 CD11R1 subpopulation. Noteworthy, sorted IgMCD21 CD11R1 B-1-like cells from eight-weeks-old pigs spontaneously secreted IgM . In addition, both non-conventional IgMCD21 B cell subpopulations, in contrast to conventional IgMCD21 B-2 cells, produced anti- IgM upon toll-like receptor (TLR) stimulation underlining their innate-like characteristics. We furthermore observed that both B-1-like subpopulations secrete 2-binding IgM upon stimulation with T cell-associated factors with highest amounts in IgMCD21CD11R1 B-1-like cells even exceeding anti- IgM levels produced by B-2 cells.

CONCLUSION

Porcine non-conventional B-1-like cells are a potent source of -binding IgM indicating a role in immunity during a critical phase of piglet rearing.