B cell memory following infection and challenge of channel catfish with Ichthyophthirius multifiliis

Area of Science:

• Immunology
• Aquatic Animal Health
• Fish Disease

Background:

• Channel catfish (Ictalurus punctatus) immune responses to parasitic infections are crucial for aquaculture.
• Understanding B cell memory is key to developing effective fish vaccines.

Purpose of the Study:

• To investigate the long-term B cell responses and memory development in channel catfish after infection with Ichthyophthirius multifiliis.
• To determine the role of IgM memory B cells in sustained humoral immunity.

Main Methods:

• Longitudinal study (3 years) of channel catfish following infection with Ichthyophthirius multifiliis.
• Quantification of serum antibody titers and antibody-secreting cells (ASCs) in skin and head kidney.
• Challenge experiments to assess immune memory.

Main Results:

• High IgM antibody titers recognizing I. multifiliis immobilization antigens declined within 1 year post-infection.
• Numbers of ASCs recognizing immobilization antigens decreased to control levels by 2-3 years post-infection.
• Upon challenge, immune fish remained protected, with increased ASCs in skin, suggesting localized memory B cell activation.

Conclusions:

• Humoral immunity in channel catfish against I. multifiliis appears to be maintained by persistent IgM(+) memory B cells.
• These memory B cells can rapidly differentiate into ASCs, primarily in the skin, upon secondary exposure.
• The findings highlight the importance of IgM memory B cells in long-term fish immunity.