For ab178846 Abcam recommends blocking in 3% milk for cleanest results in WB. Blocking with BSA gives slightly higher background.
Iba1 is a relatively minor protein of brain and is much more abundant in spleen (PMID: 8912632, PMID: 29232670). We suggest loading higher amount of brain lysate or using lower dilution of antibody for detecting signal in brain related lysates