Human CD22 cannot fully substitute murine CD22 functions in vivo, as shown in a new knockin mouse model.

CD22, an inhibitory co-receptor of the B-cell receptor, shows a B-cell-specific expression pattern and is expressed on most B-cell lymphomas. The anti-CD22 antibody Epratuzumab is in clinical trials for B-cell non-Hodgkin lymphoma and systemic lupus erythematosus, but shows a mostly unknown mode of action. We generated a new mouse model that expresses human CD22 instead of murine CD22 (Huki CD22 mice), in which human CD22 can be targeted. Expression of human CD22 on the B cells of Huki CD22 mice does not generally interfere with B-cell development. However, Huki CD22 mice show a reduction of the population of mature recirculating B cells in the bone marrow and reduced transitional and marginal zone B cells in the spleen, phenotypes resembling that of CD22-deficient mice. Similarly, enhanced BCR-induced Ca(2+) signalling is observed in Huki CD22 mice, which also mount normal immune responses toward different classes of antigens. Huki CD22 B cells show a normal anti-hCD22 antibody-mediated endocytosis. In conclusion, human CD22 cannot fully substitute for murine CD22 functions, possibly due to the changed intracellular tail of the protein or due to lower expression levels. Huki CD22 mice are a valuable new model for both antibody- and immunotoxin-mediated targeting of human CD22.

Electromyographic analysis of muscle function after latissimus dorsi tendon transfer.

The latissimus dorsi transfer is an established method for irreparable tears of the rotator cuff. The original task of the muscle is to move the arm downward and to rotate it internally. After the transfer, it has to perform the completely new function of elevating the arm. We used surface electromyography to calculate the mean values of the activity pattern in relation to the Constant score in 45 patients. We assessed patients after 6 weeks and at 6, 9, and 19 months. After the operation, most patients showed a typical activity pattern of the latissimus dorsi on electromyography, which improved in the course of the study. We also found a strong correlation between the activity pattern on electromyography and the Constant score in different areas. We conclude that the functional improvement is due to an active muscle contraction as shown on electromyography and is not just an interposition or tenodesis effect.