Oral administration of human T-cell leukemia virus type 1 induces immune unresponsiveness with persistent infection in adult rats

Abstract

The major route of human T-cell leukemia virus type 1 (HTLV-1) infection is mother-to-child transmission caused by breast-feeding. We investigated the host immune responses to orally established persistent HTLV-1 infection in adult rats. HTLV-1-producing MT-2 cells were inoculated into immunocompetent adult rats either orally, intravenously, or intraperitoneally. HTLV-1 proviruses were detected in the peripheral blood and several organs for at least 12 weeks. Transmission of HTLV-1 to these animals was confirmed by analysis of HTLV-1 flanking regions. Despite persistent HTLV-1 presence, none of the orally inoculated rats produced detectable levels of anti-HTLV-1 antibodies, whereas all intravenously or intraperitoneally inoculated rats showed significant anti-HTLV-1 antibody responses. T-cell proliferative responses against HTLV-1 were also absent in orally inoculated rats. Our findings suggest that gastrointestinal exposure of adult rats to HTLV-1-infected cells induces persistent HTLV-1 infection in the absence of both humoral and cellular immune responses against HTLV-1. This immune unresponsiveness at primary infection may subsequently affect the host defense ability against HTLV-1.

FIG. 1

Oral inoculation of HTLV-1 failed to induce antibody responses in rats. HTLV-1-producing MT-2 cells were inoculated orally (■), intravenously (▴), and intraperitoneally (•) into four, six, and three F344/N Jcl-rnu/+ rats, respectively. The anti-HTLV-1 antibody titers in the sera of these animals were determined by the particle agglutination method. Data are the averages of the titers ± standard deviations for each group. 2ⁿ, log₂.

FIG. 2

Detection of HTLV-1 provirus in orally inoculated rats by nested PCR amplifications with HTLV-1 pX (A)- and gag (B)-specific primers. (A) Tissue distribution of HTLV-1 in two orally inoculated rats, E3 (top) and E4 (bottom), at 3 months after inoculation. The presence of HTLV-1 provirus in 0.5 μg of DNA extracted from each indicated organ tissue was assessed by the nested PCR method. Rat glyceraldehyde-3-phosphate dehydrogenase (GAPDH) primers were used as an internal control. (B) DNAs (0.5 μg) from lymph nodes and peripheral blood mononuclear cells of orally inoculated rat E3 (lanes 1 and 2, respectively) and rat E4 (lanes 3 and 4, respectively) were used as templates for the nested PCR method.

FIG. 3

Lack of MT-2 cell-specific HTLV-1 flanking regions in orally inoculated rats. DNA (0.5 ng) of MT-2 cells (lane 1) and DNAs (0.5 μg) of submandibular glands of orally inoculated rat E3 (lane 2) and rat E4 (lane 3) were used as templates for nested PCR amplifications with primers amplifying the HTLV-1 flanking region of MT-2 cells (top) and primers amplifying the HTLV-1 pX region (bottom).

FIG. 4

T-cell proliferative responses against HTLV-1 antigens in inoculated rats. T-cell-enriched spleen cells from NC (naive control), E2 (orally inoculated), D6 (intravenously inoculated), and G4 (intraperitoneally inoculated) rats were incubated in the presence (solid bars) or absence (open bars) of formalin-treated syngeneic rat HTLV-1-infected cells, FPM-1, and thymidine incorporated into cells was measured. PHA was used as a positive control (hatched bars). Data represent the mean counts per minute of triplicate cultures ± standard deviations.