There are two different types of negative controls used in IHC and it is BEST practice to use both. One is a negative reagent control slide and the other is a known negative tissue control. Reviewing the primary antibody data sheet may provide suggestions not only on what is the best positive tissue, but it may also give you an indication of a good negative tissue to use as well.
Negative reagent control:
A negative reagent control can be a section of patient tissue being stained in the same manner as the positive control. There is an exception in that the primary antibody is omitted and replaced with some other solution, such as isotype, tissue culture media, buffer, or dilute non-immune serum of the same species as the primary antibody. The purpose of the negative reagent control is to ensure specificity and sensitivity of your primary antibody and rule out additional/non-specific staining when the primary antibody is removed from the protocol.
Negative tissue control:
A negative tissue control should be tissue that does NOT
contain the targeted antigen, in order to ensure there is not positive staining which may indicate non specific background staining. A known negative staining tissue may be placed on the same slide as the positive control. This tissue should receive all the same preparation and staining steps as the patient tissue. This also may be an internal control in the positive control tissue itself, where certain components of the tissue should always stain negative.