In chronic or prolonged infections, there is generally increasing expression of IgT and IgM transcripts and evidence that protective antibodies are produced that are effective in delaying disease progression, reducing disease severity, and protecting from future infection (e.g. T. byrosalmonae, S. molnari, E. leei in sea bream, nonlethal strains of C. shasta or C. shasta infections in resistant fish strains, K. thrysites, M. hunghuensis). This evidence concerns the gene CD40LG and infection.