Increased neutrophil microbicidal activity in XID mice

Neutrophils are cells that act as the first line of defense against pathogens as a crucial component of innate immunity. They migrate to sites of infection or inflammation in response to chemical signals released by other cells. They perform effector mechanisms such as phagocytosis, degranulation and emission of neutrophil extracellular networks (NETs). Furthermore, they interact with other cells of the immune system, influencing the activation and differentiation of T and B cells. B-1 cells, a subtype of B lymphocytes that produce natural antibodies, can modulate the inflammatory response through the production of IL-10. In this work we analyzed the influence of B-1 cells on the functional activity of neutrophils, using XID mice deficient in B-1 cells and consequently in the production of IL-10. The experiments were conducted as described in protocol n° 092/21 approved by CEUA/CCS/UFRJ. Our results showed that XID mice have a decrease in peripheral blood neutrophils when compared to BALB/c mice. However, in the peritoneal cavity, XID mice have a higher percentage of neutrophils with increased expression of molecules of the major histocompatibility complex class II when compared to neutrophils from BALB/c mice. Additionally, we observed that neutrophils from XID mice have a high phagocytic activity when compared to neutrophils from BALB/c mice. We also showed that neutrophils from XID mice produce higher levels of NO and ROS, molecules involved in increasing microbicidal activity. Finally, we demonstrated that neutrophils from XID mice release more NETs when compared to neutrophils from BALB/c mice. Based on our results, we suggest that in the absence of B-1 cells and their immunomodulatory action, neutrophils from XID mice exhibit increased microbicidal action that may contribute to a pro-inflammatory profile.