Enhanced virus clearance by early inducible lymphocytic choriomeningitis virus-neutralizing antibodies in immunoglobulin-transgenic mice

Abstract

Following infection of mice with lymphocytic choriomeningitis virus (LCMV), virus-neutralizing antibodies appear late, after 30 to 60 days. Such neutralizing antibodies play an important role in protection against reinfection. To analyze whether a neutralizing antibody response which developed earlier could contribute to LCMV clearance during the acute phase of infection, we generated transgenic mice expressing LCMV-neutralizing antibodies. Transgenic mice expressing the immunoglobulin mu heavy chain of the LCMV-neutralizing monoclonal antibody KL25 (H25 transgenic mice) mounted LCMV-neutralizing immunoglobulin M (IgM) serum titers within 8 days after infection. This early inducible LCMV-neutralizing antibody response significantly improved the host's capacity to clear the infection and did not cause an enhancement of disease after intracerebral (i.c.) LCMV infection. In contrast, mice which had been passively administered LCMV-neutralizing antibodies and transgenic mice exhibiting spontaneous LCMV-neutralizing IgM serum titers (HL25 transgenic mice expressing the immunoglobulin mu heavy and the kappa light chain) showed an enhancement of disease after i.c. LCMV infection. Thus, early-inducible LCMV-neutralizing antibodies can contribute to viral clearance in the acute phase of the infection and do not cause antibody-dependent enhancement of disease.

FIG. 1

Structure of the Ig transgene constructs. (A) μ heavy-chain transgene; (B) κ light-chain transgene. Filled boxes represent Ig exons, hatched boxes represent antibiotic resistance genes, and open boxes, represent cis-acting promoter elements. The heavy- and light-chain constructs were linearized prior to microinjection by using restriction endonucleases AatII and XhoI (heavy chain) and XbaI (light chain). IE, Ig heavy-chain intron enhancer; P, autologous promoter of the cloned VH gene segment; κP, consensus κ light-chain promoter.

FIG. 2

Surface expression of IgM^a on B cells of H25 and HL25 transgenic mice. IgM^a and B220 were stained on blood cells, spleen cells, and bone marrow cells of H25 transgenic mice, HL25 transgenic mice, and transgene-negative control mice (B6). Numbers in quadrants indicate percentages of gated living cells.

FIG. 3

LCMV-WE-neutralizing antibody titers in the sera of H25 and HL25 transgenic mice. H25 and HL25 transgenic mice and transgene negative control (ctrl) mice were infected i.v. with 200 PFU of LCMV-WE. Sera were collected at the indicated time points and were tested for virus-neutralizing total Ig (nonreducing conditions; closed symbols) and IgG (reducing conditions; open symbols) in an infectious focus reduction assay. Sera were prediluted 10-fold and titrated in 2-fold dilution steps. Values are for individual mice from one representative experiment of five similar experiments.

FIG. 4

H25 transgenic mice clear LCMV earlier than control mice. H25 and HL25 transgenic mice and transgene-negative control (ctrl) littermates were infected i.v. with 200 PFU of LCMV-WE. At days 1 to 10, spleens were tested for virus titers in an infectious focus formation assay. Virus titers per spleen of individual mice are indicated. The log titer of 1.7 is the detection limit of the assay. Values are for individual mice from one representative experiment of three similar experiments.

FIG. 5

CTL activity in H25 and HL25 transgenic mice. H25 and HL25 transgenic mice and transgene-negative control (ctrl) littermates were infected i.v. with 200 PFU of LCMV-WE. Eight days later, spleen cells were tested for cytolytic activity in a 5-h ⁵¹Cr release assay. MC57G target cells were labeled with the LCMV-specific peptide GP33-41 or NP396-408 or an irrelevant, H-2D^b-binding adenovirus (Adeno) peptide. Percentages of specific lysis by splenic effectors of individual mice are plotted at the indicated effector/target (E/T) ratios. Spontaneous release was below 17%. Values are for individual mice from one representative experiment of three similar experiments.

FIG. 6

Early-inducible LCMV-neutralizing antibodies in H25 mice do not enhance lethal choriomeningitis. H25 and HL25 transgenic mice were infected i.c. with 30 PFU (closed symbols) or 10⁵ PFU (open symbols) LCMV-WE. Control mice were either passively treated intraperitoneally with 200 μg of MAb KL25 4 h prior to infection or left untreated and were i.c. infected as were the Ig-transgenic mice. Survival was monitored from days 1 to 14. Each group consisted of 6 to 10 mice. Shown are results of one of two similar experiments. ctrl, control.