F05 - The Effect of Antigen Characteristics on Camelid Immunoglobulin Isotype Responses

Abstract:

Background: Camelids are the only mammalian family to produce both conventional antibodies, with a paired heavy and light chain (IgG1), and two heavy-chain only antibody (HcAb) types (IgG2 and IgG3). The binding domains of these antibodies (called VHHs or nanobodies) have significant potential as therapeutic agents due to their small size and durability. However, the factors that drive conventional versus HcAb response in camelids are currently unknown.

Hypothesis: Relative serum concentration of HcAbs versus conventional antibodies is influenced by antigen size and type, as well as individual immune response.

Animals: Banked sera from 8 research alpacas, immunized with 24 antigens

Methods: IgG production was quantified in sera using dilution ELISA. Limit titers were compared between groups by univariate analysis, based on data normality.

Results: HcAbs accounted for only ~5% of total IgG (range 0.03%-24%), with small antigens ( < 50kDa) inducing a lower overall IgG response than medium (50-100kDa; p=0.027) and large (>100kDa; p=0.004) antigens. More specifically, significantly less IgG2 and IgG3 were produced in response to small versus medium (p=0.047) and small compared to large antigens (p=0.039), respectively. Descriptive assessment suggested that carbohydrate and glycolipid antigens induced a lower antibody response than protein-based antigens, but statistical analysis was limited by sample size. Additionally, inter-individual variation in immune response was observed between animals.

Conclusions and Clinical Importance: Antigen size affected relative HcAb and conventional antibody responses in alpacas. Although further assessment is necessary to characterize the immune response to non-protein antigens, these data may direct epitope selection for novel immunotherapeutic development.