Abstract
Background:
Understanding the distribution of antibodies in the bloodstream is critical for advancing diagnostic and therapeutic approaches in veterinary and comparative immunology. While most studies focus on plasma antibodies, the presence and role of membrane-bound immunoglobulins remain underexplored, particularly in equine species like the Jabe horse.

Aim:
The aim of the research was to analyze the quantity of antibodies in plasma and on blood cells, with a view to their potential future applications.

Methods:
Blood samples were collected from Jabe horses and separated into plasma and cellular components. A specific technique was developed to isolate immunoglobulins from both plasma and blood cell membranes. The concentrations of different immunoglobulin classes (IgA, IgM, IgE, IgG, and IgD) were measured using immunoassays. Special attention was given to aged erythrocytes to examine antibody accumulation over time.

Results:
The antibody concentration in plasma was generally higher than on blood cell membranes. However, the membrane-bound fractions of IgA, IgM, and IgE ranged from 106% to 139.7%, indicating significant membrane association. IgG levels in the supernatant were over 60% lower than in plasma, suggesting selective membrane binding or sequestration. Notably, IgD was predominantly membrane-bound, with concentrations many times higher than in the supernatant. A marked increase in membrane-bound immunoglobulins was observed on aged erythrocytes, highlighting a possible age-dependent accumulation. Furthermore, the content of other membrane-associated proteins correlated with their absolute concentrations in plasma.

Conclusion:
The study reveals that immunoglobulins are not only present in plasma but also significantly associated with blood cell membranes in Jabe horses. The high levels of membrane-bound IgD and the accumulation of antibodies on aged erythrocytes suggest functional or regulatory roles yet to be fully understood. The newly proposed method for antibody isolation from both plasma and cellular fractions opens opportunities for further immunological research and potential clinical applications in veterinary medicine.

Key words: Blood components; Erythrocytes; Immunoassay; Immunoglobulins; Membrane transport.