IgM has a better relative distribution in inflammation sites and tumor tissues than IgG.

Immunoglobulins (Igs) play a crucial role in host's defense and in developing therapies against inflammatory diseases and cancer. Herein, we first studied the relative distribution of IgM and IgG in mouse models with acute or chronic inflammation. We found that IgM showed a more selective distribution towards inflammation sites than IgG. Similarly, in a tumor-bearing mouse model, IgM showed a higher tumor-to-blood or -to healthy organs ratio than IgG. We hypothesized that the difference in the sizes between IgM and IgG may have contributed to the differences in their relative distribution, which was supported by using an IgG nanoparticle system that was similar to IgM in size. To confirm the findings in clinics, we investigated IgM and IgG levels in the blood and bronchoalveolar lavage fluid (BALF) of patients diagnosed with fungal pneumonia and showed that the relative distribution of IgM was significantly higher than IgG in the BALF samples as compared to that in serum. Such an understanding of our immune system at the nano-level may help us develop more effective biotechnological interventions against inflammatory diseases and cancers.