Low maternal CD4 count at inception of gestational cytomegalovirus (CMV) infection and impaired humoral response: effect on congenital CMV infection in the guinea pig

Transplacental murine cytomegalovirus infection in the brain of SCID mice

BACKGROUND

Congenital cytomegalovirus (CMV) infection is the most common congenital viral infection in humans and the major nonhereditary cause of central nervous system (CNS) developmental disorders. Previous attempts to develop a murine CMV (MCMV) model of natural congenital human CMV (HCMV) infection have failed because MCMV does not cross the placenta in immunocompetent mice.

RESULTS

In marked contrast with immunocompetent mice, C.B-17 SCID (severe combined immunodeficient) mice were found to be highly susceptible to natural MCMV transplacental transmission and congenital infection. Timed-pregnant SCID mice were intraperitoneally (IP) injected with MCMV at embryonic (E) stages E0-E7, and vertical MCMV transmission was evaluated using nested polymerase chain reaction (nPCR), in situ hybridization (ISH) and immunohistochemical (IHC) assays. SCID mouse dams IP injected at E0 with 102 PFU of MCMV died or resorbed their fetuses by E18. Viable fetuses collected at E18 from SCID mice IP injected with 102-104 PFU of MCMV at E7 did not demonstrate vertical MCMV transmission. Notably, transplacental MCMV transmission was confirmed in E18 fetuses from SCID mice IP injected with 103 PFU of MCMV at stages E3-E5. The maximum rate of transplacental MCMV transmission (53%) at E18 occurred when SCID mouse dams were IP injected with 103 PFU of MCMV at E4. Congenital infection was confirmed by IHC immunostaining of MCMV antigens in 26% of the MCMV nPCR positive E18 fetuses. Transplacental MCMV transmission was associated with intrauterine growth retardation and microcephaly. Additionally, E18 fetuses with MCMV nPCR positive brains had cerebral interleukin-1alpha (IL-1alpha) expression significantly upregulated and cerebral IL-1 receptor II (IL-1RII) transcription significantly downregulated. However, MCMV-induced changes in cerebral cytokine expression were not associated with any histological signs of MCMV infection or inflammation in the brain.

CONCLUSION

Severe T- and B-cell immunodeficiencies in SCID mice significantly enhance the rate of natural MCMV transplacental transmission and congenital infection. During gestation MCMV exhibits a tissue tropism for the developing brain, and vertical MCMV transmission is correlated with fetal growth retardation and abnormal cerebral proinflammatory cytokine expression. These data confirm that natural vertical MCMV infection in SCID mice constitutes a useful new experimental rodent model of congenital HCMV infection.

Analysis of mature guinea pig T cells with a monoclonal antibody directed against a framework determinant of the T-cell receptor for antigen

Rats were immunized with guinea pig T lymphocytes and the spleen cells were fused with cells of a mouse myeloma line. The resulting hybrids were screened for the production of antibodies selectively reacting with guinea pig T cells. The monoclonal antibody (MoAb) H159 was analysed in detail because it bound to T lymphocytes, but not to B lymphocytes or macrophages. Cellular ELISA, cytofluorometry and immunohistology revealed that the antigen detected by H159 is selectively expressed on the majority of peripheral mature T lymphocytes (about 95%). In contrast, it stained only a minor population of thymocytes in FACS analysis. H159 precipitated from NP40 lysate of T cells a protein with a molecular weight of about 90 kDa when separated under non-reducing conditions in SDS-PAGE. Under reducing conditions bands with molecular weights of about 50 kDa were found. After binding to anti-rat Ig coated beads, the MoAb H159 had a mitogenic effect for guinea pig T lymphocytes whereas soluble MoAb H159 in the presence or absence of macrophages was not mitogenic. The cellular expression and molecular characteristics of the H159 antigen together with the mitogenic activity of the antibody for T cells indicate that the MoAb H159 recognizes the guinea pig T-cell receptor for antigen via a constant region determinant.