T-cell-dependent antibody responses in the rat: forms and sources of keyhole limpet hemocyanin matter

The T-cell-dependent antibody response (TDAR) is a functional assay used in immunopharmacology and immunotoxicology to assess ability to mount an antibody response to immunization. Keyhole limpet hemocyanin (KLH) is extensively used as the immunogen of choice in non-clinical and clinical settings. Native KLH is comprised of high molecular weight (HMW; 4-8 MDa) assemblies of KLH subunit dimers (> 600-800 kDa). It is not known how the different forms (HMW vs subunit) and manufacturing processes (commercial sources) may impact the nature of anti-KLH immune responses (e.g. magnitude and inter-animal variability). Anti-KLH IgM and IgG responses were studied in Sprague-Dawley rats immunized with different forms and commercial sources of KLH: 100 µg of HMW KLH from two different sources or subunit KLH from three different sources. Biophysical and biochemical analyses were conducted to characterize the KLH formulations. Anti-KLH IgM and IgG responses were measured using a proprietary indirect quantitative electrochemiluminescence immunoassay. The HMW KLH preparations showed a greater number of sub-visible particles (2-150 µm size range) than the subunit KLH preparations. All HMW KLH and all subunit KLH were equivalent on SEC (hydrodynamic volume), PAGE (size and charge), and SDS-PAGE (molecular radius). Robust primary and secondary anti-KLH responses were detected for both sources of HMW KLH. The subunit KLH immunizations resulted in lower IgG and IgM responses compared to the HMW KLH, with the exception of Stellar Biotechnologies subunit KLH that produced both robust primary and secondary responses, which approached the HMW KLH responses. Inter-animal variability for IgM and IgG responses was lower with HMW KLH than with subunit KLH. In conclusion, different forms and commercial sources of KLH were associated with different magnitudes and inter-animal variability in IgM and IgG responses, a critical finding to take into consideration when designing TDAR studies for robust immunotoxicology or immunopharmacology testing.