Table 1.

Microscopic lesions and viral antigen distribution in tissues from chickens intranasally inoculated with the Mexican H7N3 HPAI virus detected at 2 days p.c.^a

Tissue	Histopathology scoreb	Lesions	IHC scorec	Cell types expressing virus antigen
Nasal cavity	+++	Epithelial cell necrosis and desquamation, rhinitis, sinusitis, lymphocytic infiltrate	++	Vascular endothelial cells, epithelial cells, mononuclear cells, necrotic debris
Trachea	++	Tracheitis, lymphocytic infiltrate	+++	Vascular endothelial cells, epithelial cells, cellular debris, cells of the tracheolateralis muscle
Lung	++ to +++	Interstitial pneumonia, bronchitis, edema, congestion, hemorrhage, necrosis, monocytic infiltrate	+++	Epithelium of air capillaries, mononuclear cells, necrotic debris
Air sac	++	Airsacculitis, monocytic infiltrate	+++	Epithelial and mononuclear cells
Comb	+++	Edema, hemorrhages, necrosis	+++	Vascular endothelial cells, mononuclear cells, necrotic debris
Eyelid	+++	Subcutaneous edema, epidermal and feather follicle necrosis	+++	Vascular endothelial cells, mononuclear cells, feather follicle epithelium
Heart	−	Myocyte necrosis	+	Myocytes
Brain	+ to ++	Neuronal necrosis, gliosis, encephalomalacia, chromatolysis of the Purkinge cell layer, lymphoplasmacytic infiltrate	+ to ++	Neurons, glial cells
Esophagus	−	−	+	Mononuclear cells in submucosa
Proventriculus	++	Edema and inflammatory infiltration in submucosa	+++	Mononuclear cells in submucosa
Ventriculus	−	−	+	Mononuclear cells in submucosa
Intestine	+ to ++	Lymphohistiocytic infiltration in submucosa, hemorrhage, epithelial necrosis	+	Mononuclear cells in lymphoid-associated tissue, vascular endothelial cells
Cecal tonsils	++	Hemorrhage, lymphocyte depletion, necrosis	++	Macrophages
Pancreas	+	Degeneration of individual pancreatic acinar cells	−	−
Liver	++	Lymphohistiocytic hepatitis	++	Kupffer cells, hepatocytes, necrotic debris, vascular endothelial cells
Spleen	+++	Lymphoid depletion, necrosis, splenitis, hyperplasia of macrophage-phagocytic cells	++ to +++	Mononuclear cells, necrotic debris, vascular endothelial cells
Thymus	+ to +++	Lymphocyte necrosis and apoptosis, lymphocyte depletion, hemorrhage	+ to +++	Histiocytes
Cloacal bursa	+ to ++	Lymphocyte necrosis and apoptosis, lymphocyte depletion, phagocytic hyperplasia, necrosis, hemorrhage	− to ++	Mononuclear cells
Harderian gland	+		++	Mononuclear cells
Kidney	− to +	Tubular epithelial necrosis	− to ++	Tubular epithelial cells
Gonads	+	Necrosis, lymphoplasmacytic infiltrate	+	Mononuclear and interstitial cells
Adrenal gland	− to +++	Necrosis, mononuclear infiltrate, hemorrhages	−	Corticotrophic and corticotropic cells
Muscle	+	Congestion	−	−

^aTissues were collected from 2 birds per age group (n = 4).

^bHistologic lesion scores by HE staining: −, no lesions; +, mild lesions; ++, moderate lesions; +++, severe lesions.

^cIHC staining scores: −, no antigen staining; +, infrequent staining; ++, common staining; +++, widespread staining.