# The Class I Scavenger Receptors CD5 and CD6 Play a Role in the Early Peritoneal Immune Response to Echinococcus granulosus Tegumental Antigens

## TL;DR

CD5 and CD6 receptors help the immune system detect and respond to a parasitic worm, Echinococcus granulosus, in the early stages of infection.

## Contribution

CD5 and CD6 are shown to play a direct role in immune recognition of E. granulosus antigens and influence early immune responses.

## Key findings

- CD5 and CD6 deficiency impairs PSEx antigen binding by peritoneal B cells and macrophages.
- Lack of CD5 or CD6 alters immune cell activation and shifts cytokine profiles toward Th2.
- Deficient mice show impaired early antibody production and altered CD80/CD86 expression.

## Abstract

Scavenger Receptors (SRs) comprise a structurally diverse group of pattern recognition receptors (PRRs) involved in sensing non-self (microbial-associated molecular patterns) or altered-self ligands. CD5 and CD6 are class I SRs (SR-I) preferentially expressed by lymphoid cells and characterized by the presence of several tandem scavenger receptor cysteine-rich (SRCR) domain repeats. Both receptors interact with diverse microbial structures, including tegumental antigens from Echinococcus granulosus sensu lato (s.l.), the cestode parasite responsible for cystic echinococcosis (CE). This is notable as very few PRRs are currently known to detect parasitic helminths and because the infusion of recombinant soluble CD5 and CD6 proteins has shown prophylactic effects in murine secondary CE. Herein, the role of CD5 and CD6 in early immune responses to E. granulosus s.l. tegumental antigens (PSEx) was analyzed using CD5 (Cd5−/−) and CD6 (Cd6−/−)-deficient mice. Peritoneal B cells and macrophages from wild-type mice displayed specific and dose-dependent PSEx binding, which was impaired in those from Cd5−/− and Cd6−/− mice, supporting direct and/or indirect roles in parasite recognition. Additionally, in vivo exposure of peritoneal exudate cells (PECs) from Cd5−/− and Cd6−/− mice to PSEx showed altered activation profiles, including changes in CD80/CD86 expression, impaired early production of natural polyreactive antibodies, and cytokine shift from a Th1/Th17 to a Th2 profile. These findings strongly support the involvement of CD5 and CD6 receptors in the early immune recognition of E. granulosus s.l. antigens by PECs and influence immune responses critical for host resistance, highlighting their relevance in host–parasite interactions.