Granules of blood eosinophils are stained directly by anti-immunoglobulin fluorescein isothiocyanate conjugates.

This research studied how anti-immunoglobulin fluorescein isothiocyanate (FITC) conjugate directly stains the granules of blood eosinophils in several species including cats, pigs, horses, cattle, dogs, sheep, birds, and humans.

Study on Direct Staining of Eosinophils

The researchers found out that anti-immunoglobulin FITC conjugates directly stain the granules of blood eosinophils. This was observed when feline blood smears were tested for evidence of feline leukemia virus (FeLV). The study looked at:

• The immunofluorescence of the eosinophils under an antibody test designed to reveal the presence of FeLV.
• The fact that this staining phenomenon by FITC conjugates wasn’t just restricted to feline samples but was also observed in blood smears from pigs, horses, cattle, dogs, sheep, birds, and humans.

Exclusivity of FITC Staining to Eosinophils

Among other cells, eosinophils were the only ones to exhibit this staining effect:

• Other cells like neutrophils, lymphocytes, and platelets from the same variety of species tested showed no such direct staining by the FITC conjugates.
• Thus, the study confirmed that the FITC staining is exclusive to the granules of eosinophils among the tested cells.

Implications for Detection of Feline Leukemia Virus (FeLV)

The findings of this study also have implications for the technique used to detect feline leukemia virus:

• Direct FITC staining of eosinophils does not pose a problem for the immunofluorescent test used to detect FeLV infection in cats.
• This is because the eosinophils, which can easily be recognized, can be excluded from the spectrum of cells to be interpreted for the test.
• Exclusion prevents misinterpretation of positive staining FeLV infection when the staining is actually due to eosinophils.