Immunobiological role of llama heavy-chain antibodies against a bacterial β-lactamase

• Published in: Veterinary Immunology and Immunopathology Vol. 117; no. 3; pp. 173 - 182
• Main Authors: Ferrari, A., Rodríguez, M.M., Power, P., Weill, F.S., De Simone, E.A., Gutkind, G., Leoni, J.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15-06-2007
• Subjects: animal models; animal physiology; Animals; antibodies; Antibody Affinity; Antigen-Antibody Reactions; Bacteria; beta-lactamase; beta-Lactamases - genetics; beta-Lactamases - immunology; beta-Lactamases - metabolism; Camelidae; Camelids, New World - immunology; disease resistance; enzyme activity; Enzyme inhibition; enzyme inhibitors; Enzyme-Linked Immunosorbent Assay; Heavy-chain antibodies; immune response; immune system; immunization; Immunoglobulin Heavy Chains - immunology; Immunoglobulin Heavy Chains - metabolism; Immunoglobulin Isotypes - immunology; Immunoglobulin Isotypes - metabolism; immunoglobulins; in vivo studies; Lama; Lama glama; Llama; llamas; Rabbits; Recombinant Proteins - immunology; Recombinant Proteins - metabolism; Regression Analysis; South American camelids; β-Lactamase; HCAbs; rVHHs; OPD; FRs; HRPO; CH 1; kDa; β-Lactamase; Heavy-chain antibodies; South American camelids; Llama; ANOVA; SACs; Enzyme inhibition; FA; CDR3
• ISSN: 0165-2427; 1873-2534; 1365-2567
• DOI: 10.1016/j.vetimm.2007.03.003

In 1993, a fraction of antibodies (Abs) devoid of L chain was found naturally occurring in the Camelidae. They were found to lack L chains, as well as the first constant heavy-chain domain (CH
1) and therefore they were named “heavy-chain Abs” (HCAbs). Subsequent studies focused on the functional, structural and biochemical properties of recombinant variable fragments (rVHHs) of HCAbs. It was stated that rVHHs have an augmented capacity to interact with “partially hidden” epitopes, like enzymes active sites, and have an increased stability to thermal and chemical aggression. It has been suggested that these unconventional Abs could represent an evolutionary advantage, being more efficient than conventional Abs to inhibit microbial enzymes, and thus exerting a more protective immune response against pathogens. The present work focuses on the immunobiological role of HCAbs, in their capacity to inhibit microbial enzymes. Two animal models were selected, comprising a model for common vertebrates without HCAbs (rabbits), and a model for vertebrates with both conventional and unconventional Abs (
Lama glama). A recombinant bacterial β-lactamase (CTX-M-2) was selected as the microbial enzymatic antigen. After conventional immunization schedules, neither serum titers nor serum inhibitory capacity showed significant differences when rabbits and llamas were compared. These results indicate that the a priori assumption that the adaptive immune system of camelids could be better “prepared” to respond to bacterial enzymes because of the presence of HCAbs, is not always accurate. Furthermore, when the different llama antibody isotypes and subclasses were purified, it was demonstrated that the inhibitory capacity of total serum was due exclusively to IgG
1. HCAbs not only failed to inhibit CTX-M-2, but instead they activated its enzymatic activity. Altogether, these results indicate that the hypotheses extrapolated from the rVHHs properties need to be revised; the real role of HCAbs in vivo remains unknown, as well as their evolutionary cause.