Refinement of the rat acetylcholine receptor-specific passive transfer myasthenia gravis model using subcutaneous injections: an update to the guidelines

The passive transfer model of myasthenia gravis (PTMG) reflects the effector phase of the human condition and is induced in female rats using monoclonal antibodies. The current guideline recommends administration of monoclonal antibodies (mAb) such as mAb35 via intraperitoneal (I.P.) or intravenous (I.V.) injection, offering rapid absorption, but posing challenges such as injection placement and, in the case of I.P., animal discomfort. In this study, we investigated the suitability of subcutaneous (S.C.) administration as an alternative to I.P. in the rat PTMG model. Female rats were injected with 20 pmol mAb35 /100 g body weight (BW), either I.P. or S.C. and euthanized 48 h post-immunization, or S.C. with 20 or 40 pmol mAb35 /100 g BW and euthanized 48- or 72-hours post-immunization. Control animals received 0.5 mg/kg IgG1 isotype control S.C. or I.P. Muscle weakness, weight loss and clinical manifestations were assessed daily. Additionally, decrement-inducing curare dose and AChR content in the tibialis anterior (TA) were determined using electromyography and radioimmunoassay (RIA) respectively. S.C. mAb35 administration induced body weight loss and MG symptoms comparable to I.P. administration. However, I.P. injection presented a risk of misplacement, making it potentially a less reliable administration method. While MG characteristics were observed regardless of mAb35 dose and route, variability of clinical parameters and TA AChR content differed between approaches. S.C. induction of disease was verified using a different batch of mAb35 with a dose of 40 pmol/100 g BW S.C administered. We demonstrated that S.C. injection offers a consistent induction of PTMG, establishing it as a refined, effective alternative to I.P. administration by reducing procedural invasiveness and improving consistency in symptom onset.