The direct method is a one-step staining method. This method consists of using a labeled antibody, such as fluorescein isothiocyanate (FITC) conjugated antiserum, enzyme, or alkaline phosphate that reacts directly with a specific antigen in tissue sections.
The label type in the direct method is commonly a FITC label. This technique is designed to be simple and fast given that it uses only one antibody.
A drawback to this method is that it is less sensitive since the method excludes signal amplification actions, which are helpful when there are minimal epitope sites available. One other drawback when you are using a FITC labeled antibody is that the fluorescent color spectrum for FITC is around 488 nm and so is autofluorescence.