FITC-conjugated anti-rat primary antibodies are directly labeled immunoreagents that combine a rat antigen-specific immunoglobulin with fluorescein isothiocyanate (FITC), enabling single-step detection of target proteins in flow cytometry and related applications. They are distinct from FITC-conjugated anti-rat secondary antibodies, which are raised in another host to detect rat immunoglobulins; the primary format discussed here involves the antigen-binding immunoglobulin itself, covalently linked to the fluorophore.

The FITC Fluorophore and Spectral Properties

FITC is a green-emitting xanthene dye with an excitation maximum of approximately 490–495 nm and an emission maximum of approximately 520–528 nm. It is efficiently excited by the 488 nm blue laser line standard on most flow cytometers and is detected using an optical filter centered near 530 nm, such as a 525/40 nm or 530/30 nm bandpass filter. FITC remains one of the most widely used fluorophores because of its long history, low cost, and broad compatibility with existing instrumentation, although it is less bright and more prone to photobleaching than newer green-emitting dyes such as Alexa Fluor 488.

Applications

FITC-conjugated anti-rat primary antibodies are validated primarily for flow cytometry, with each lot quality control tested by immunofluorescent staining and flow cytometric analysis. The recommended usage for directly conjugated primary antibodies is typically 0.1–1 µg per 10⁶ cells in 100 µL volume, though each investigator should titrate the reagent for optimal performance in their specific application. Beyond flow cytometry, these reagents support immunofluorescence microscopy and, for some clones, immunohistochemistry on frozen or paraffin-embedded sections. FITC-labeled anti-rat IgG reagents can also be used to verify specific binding of rat IgG to its receptor by first incubating cells with the primary rat antibody. In multicolor panels, the green emission of FITC is well separated from the orange (PE) and far-red (APC) channels, facilitating panel design alongside these common fluorophores.