A. Kipar et al., CELLULAR COMPOSITION, CORONAVIRUS ANTIGEN EXPRESSION AND PRODUCTION OF SPECIFIC ANTIBODIES IN LESIONS IN FELINE INFECTIOUS PERITONITIS, Veterinary immunology and immunopathology, 65(2-4), 1998, pp. 243-257
Twenty-three cats with spontaneous feline infectious peritonitis (FIP)
were examined by light microscopy including immunohistology and histo
chemistry in order to determine the cellular composition and the expre
ssion of viral antigen in lesions in FIP. Furthermore, the presence of
plasma-cells producing coronavirus-specific antibodies was evaluated
in situ. Macrophages and neutrophils were demonstrated by an antibody
against calprotectin (leukocyte protein L1, myeloid/histiocyte antigen
), neutrophils were recognized due to their chloroacetate esterase act
ivity, and B- and T-lymphocytes were identified by antibodies against
the CD3 antigen and the CD45R antigen, respectively. Expression of vir
al antigen was immunohistologically demonstrated by a monoclonal antib
ody (mAb) against coronavirus while coronavirus-specific antibodies in
situ were identified by the application of feline coronavirus prior t
o the coronavirus antibody. Lesions were classified as diffuse alterat
ions at serosal surfaces, granulomas with areas of necrosis, granuloma
s without extended necrosis, focal and perivascular lymphoplasmocytic
infiltrates, and granulomatous-necrotizing vasculitis. Diffuse alterat
ions on serosal surfaces were represented either by activated mesothel
ial cells with single coronavirus antigen-bearing macrophages or by la
yers of precipitated exudate containing single to numerous granulomas
with areas of necrosis. In liver and spleen, the exudate was often und
erlaid by a small band of subcapsular B-cells with an occasional plasm
a-cell producing coronavirus-specific antibodies. In other locations,
a variably broad and of B-cells and plasma-cells, often infiltrating b
etween underlying muscle fibers, separated the exudate from the unalte
red tissue. Some of these plasma-cells were positive for coronavirus-s
pecific antibodies. In granulomas with areas of necrosis, the central
necrosis was surrounded by macrophages usually expressing considerable
amounts of viral antigen. Few B-cells and plasma-cells were found in
the periphery. In granulomas without extended necrosis, the number of
macrophages were lower. Only few macrophages expressing low amounts of
viral antigen were present. B-cells and plasma-cells formed a broad r
im. Few plasma-cells stained positive for coronavirus-specific antibod
ies. In both types of granulomas, few neutrophils were found between m
acrophages. Few T-cells were seen scattered throughout the lesions. Fo
cal and perivascular lymphoplasmocytic infiltrates were mainly seen in
omentum and leptomeninx. B-cells were the predominant cells; some pla
sma-cells were positive for coronavirus-specific antibodies. Viral ant
igen was not readily detected in these alterations. Granulomatous-necr
otizing vasculitis was occasionally found in kidneys and leptomeninx.
It was dominated by macrophages which often stained strongly positive
for coronavirus antigen. Different types of alteration were often seen
in the same animal and even the same tissue. There was no obvious cor
relation between the cat's age, gross pathological changes, and the hi
stological types of alteration. Single plasma-cells positive for coron
avirus-specific antibodies were found around blood vessels distant fro
m inflammatory alterations, within the lung parenchyma, as infiltratin
g cells in the mucosa of the small intestine, and in spleen and mesent
eric lymph node. Results show that alterations in FIP are heterogeneou
s concerning cellular composition and expression of viral antigen. The
dominance of B-cells in part of the lesions together with the presenc
e of plasma-cells positive for coronavirus-specific antibodies indicat
e that these cells may play a role in the maintenance of inflammatory
processes in FIP. (C) 1998 Elsevier Science B.V. All rights reserved.