Early pathogenesis of transmucosal feline immunodeficiency virus infection

Abstract

To identify the early target cells and tissues in transmucosal feline immunodeficiency virus (FIV) infection, cats were exposed to a clade C FIV isolate via the oral-nasal or vaginal mucosa and multiple tissues were examined by virus isolation coculture (VI), DNA PCR, catalyzed tyramide signal-amplified in situ hybridization (TSA-ISH), and immunohistochemistry between days 1 and 12 postinoculation (p.i.). FIV RNA was detected in tonsil and oral or vaginal mucosa as early as 1 day p.i. by TSA-ISH and in retropharyngeal, tracheobronchial, or external iliac lymph nodes and sometimes in spleen or blood mononuclear cells by day 2, indicating that regional and distant spread of virus-infected cells occurred rapidly after mucosal exposure. By day 8, viral RNA, DNA, and culturable virus were uniformly detected in regional and distant tissues, connoting systemic infection. TSA-ISH proved more sensitive than DNA PCR in detecting early FIV-infected cells. In mucosal tissues, the earliest demonstrable FIV-bearing cells were either within or subjacent to the mucosal epithelium or were in germinal centers of regional lymph nodes. The FIV(+) cells were of either of two morphological types, large stellate or small round. Those FIV RNA(+) cells which could be colabeled for a phenotype marker, were labeled for either dendritic-cell-associated protein p55 or T-lymphocyte receptor antigen CD3. These studies indicate that FIV crosses mucous membranes within hours after exposure and rapidly traffics via dendritic and T cells to systemic lymphoid tissues, a pathway similar to that thought to occur in the initial phase of infection by the human and simian immunodeficiency viruses.

FIG. 1.

RNA ISH utilizing either Vector red or BCIP-nitroblue tetrazolium chromogen and methyl green counterstain. (A) FIV⁺ cell (arrow) in the oral epithelium (oe) of cat 3797 1 day p.i. Magnification, ×400. (B) FIV⁺ cell (arrow) in the tonsillar parenchyma adjacent to the crypt epithelium (ce) of cat 3791 2 days p.i. Magnification, ×100. (C) FIV⁺ cell (arrow) in the intestinal epithelium (ie) of a villus (v) from the jejunum of cat 3791 2 days p.i. Magnification, ×400. lp, lamina propria. (D) Numerous FIV⁺ cells (arrows) in the germinal center (gc) of a follicle (f) from the retropharyngeal LN from cat 3795 10 days p.i. Magnification, 100. (E) FIV⁺ cell (arrow) with DC morphology in the vaginal submucosa (sm) of cat 3598 2 days p.i. Magnification, ×400. vm, vaginal mucosa. (F) Several FIV⁺ cells (arrows) in the parafollicular region of the medial iliac LN from cat 3853 4 days p.i. Magnification, ×200.

FIG. 2.

(A) Illustration demonstrating target tissue infection frequency between 1 and 3 days after oral-nasal FIV exposure as determined by DNA PCR and RNA ISH. FIV was most frequently identified in tissues of the upper gastrointestinal tract (GI) (62% of the animals). The next most frequently observed FIV-infected tissues were oral mucosa (OM), retropharyngeal LN (RLN), and PBMC (50% of the animals). (B) Illustration demonstrating target tissue infection frequency between 1 and 3 days after vaginal FIV exposure as determined by DNA PCR and RNA ISH. FIV was most frequently identified in tissues of the vaginal mucosa (VM) and spleen (S) (40% of the animals). The next most frequently observed FIV-infected tissues were medial iliac LN (ILN), sacral LN (SLN), and PBMC (20% of the animals). Arrows (both panels), flow of lymphatic drainage from the mucosal tissues to regional lymphoid tissues to lymphatic trunks and/or ducts, which ultimately empty into the venous circulation (PBMC). BM, bone marrow; CmLN, cranial mediastinal LN; JT, jugular trunk; LT, lumbar trunk; SmLN, submandibular LN; T, thymus; TbLN, tracheobronchial LN; TD, thoracic duct.

FIG. 3.

Dual RNA ISH and immunohistochemistry utilizing Vector red for FIV RNA probe detection, silver-enhanced immunogold for phenotypic identification, and methyl green counterstain. (A) p55⁺ FIV⁺ DC (arrows) in the vaginal submucosa (sm) of cat 3826 6 days p.i. Magnification, ×400. vm, vaginal mucosa. (B) FIV⁺ cell (arrow) and two FIV-uninfected MAC387⁺ macrophages (arrowheads) in the vaginal submucosa of cat 3826 6 days p.i. Magnification, ×200. (C) p55⁺ FIV⁺ cell (arrow) in the oral submucosa of cat 3804 10 days p.i. Magnification, ×200. oe, oral epithelium. (D) CD3⁺ FIV⁺ T cells (arrows) and several FIV-uninfected CD3⁺ cells (arrowheads) in the tonsillar parenchyma of cat 3795 10 days p.i. Magnification, ×400. (E) MAC387⁺ FIV⁺ macrophage (arrow) in a follicle (f) adjacent to the subcapsular sinus (scs) region of the retropharyngeal LN from cat 3815 3 days p.i. Magnification, ×400. (F) CD3⁺ FIV⁺ T cell (arrow) and several FIV-uninfected CD3⁺ T cells (arrowheads) in the PBMC of cat 3804 10 days p.i. Magnification, ×400.