Therapeutic efficacy of high-dose intravenous immunoglobulin in Mycobacterium tuberculosis infection in mice

Abstract

Intravenous immunoglobulin (IVIg) is used to treat patients with primary antibody deficiencies and, at high doses, to treat a range of autoimmune and inflammatory disorders. With high-dose IVIg (hdIVIg), immunomodulatory mechanisms act on a range of cells, including T cells, B cells, and dendritic cells. Here, we demonstrate that the treatment of M. tuberculosis-infected mice with a single cycle of hdIVIg resulted in substantially reduced bacterial loads in the spleen and lungs when administered at either an early or late stage of infection. Titration of the IVIg showed a clear dose-response effect. There was no reduction in bacterial load when mice were given equimolar doses of another human protein, human serum albumin, or maltose, the stabilizing agent in the IVIg preparation. HdIVIg in vitro had no inhibitory effect on the growth of M. tuberculosis in murine bone marrow-derived macrophages. In addition, the effect of hdIVIg on bacterial loads was not observed in nude mice, suggesting the involvement of conventional T cells. Analysis of T cells infiltrating the lungs revealed only small increases in CD8(+) but not CD4(+) T-cell numbers in hdIVIg-treated mice. The mechanism of action of hdIVIg against tuberculosis in mice remains to be determined. Nevertheless, since hdIVIg is already widely used clinically, the magnitude and long duration of the therapeutic effect seen here suggest that IVIg, or components of it, may find ready application as an adjunct to therapy of human tuberculosis.

FIG. 1.

Effect of IVIg on the growth of M. tuberculosis in mice. C57BL/6 mice were infected with H37Rv and then received two identical i.p. injections of IVIg at either 6 and 24 h or 3 and 5 days postinfection. Viable counts were conducted on spleen and lungs on days 0, 42, and 85 postinfection. Results are expressed as means ± the standard error of the mean (SEM) of five mice per group and are representative of at least four independent experiments. *, P < 0.01 as measured by Student's t test.

FIG. 2.

Analysis of pulmonary immune response. (A) Cells extracted from the lungs of C57BL/6 mice at day 42 postinfection were stained for surface expression of CD4, CD8, CD3ɛ, or the activation marker CD44. Results show cells pooled from the lungs of five mice per group and are representative of three independent experiments. (B) Lung sections of IVIg-treated or control mice were stained with hematoxylin and eosin at day 42 postinfection. Shown at 100× and 400× magnifications.

FIG. 3.

Dose response of IVIg on M. tuberculosis in mice. BALB/c mice were infected i.v. with H37Rv and treated i.p. on day 16 postinfection with saline (control) or with 0.1 g/kg, 0.5 g/kg, 1 g/kg, or normal dose (2 g/kg) IVIg. Viable counts were conducted on day 42 postinfection. Results are expressed as means ± SEM of five mice per group.

FIG. 4.

Effect of late treatment with IVIg on the growth of M. tuberculosis in mice. C57BL/6 mice were infected i.v. with H37Rv. Viable counts were conducted on lungs and spleens on days 0, 42, and 85 postinfection to monitor the course of the infection. Late treatment with IVIg was administered i.p. on day 108 postinfection, and viable counts were conducted on day 133. Results are expressed as means ± SEM of five mice per group and are representative of two independent experiments. Similar results were observed when this experiment was repeated with IVIg given on day 60 postinfection.

FIG. 5.

Effect of IVIg or human serum albumin or maltose on growth of M. tuberculosis in mice. BALB/c mice were infected with H37Rv and received two identical i.p. injections of saline (controls), IVIg, human serum albumin, or maltose on days 3 and 5 postinfection. Viable counts were conducted on spleen and lungs at days 83 (panels A and B show the results of experiments with human serum albumin) or 70 (panels C and D show the results of experiments with maltose). Results are expressed as means ± SEM of five mice per group and are representative of two independent experiments. **, P < 0.01; *, P < 0.05 as measured by Student's t test.

FIG. 6.

Effect of IVIg on growth of M. tuberculosis in macrophages. Murine C57BL/6 BMMφ were infected with H37Rv at a multiplicity of infection of 2:1 for 6 h and maintained in either control medium or medium containing 25 mg/ml IVIg. Viable counts were conducted at days 0, 3, and 6 postinfection. Results are expressed as means ± SEM of triplicate wells and represent three independent experiments.

FIG. 7.

Effect of IVIg on the growth of M. tuberculosis in athymic mice. Athymic mice (BALB/c nu⁻/nu⁻ littermates) were infected IV with H37Rv and then treated i.p. with IVIg. Controls received 0.2 ml saline i.p. Viable counts were conducted on days 0, 22, and 40 postinfection. Results are expressed as means ± SEM of five mice per group.