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Infection and Immunity, May 2003, p. 2938-2940, Vol. 71, No. 5
0019-9567/03/$08.00+0 DOI: 10.1128/IAI.71.5.2938-2940.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

T-Cell-Deficient Mice
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520,1 Center for Comparative Medicine, University of California, Davis, California 956162
Received 26 November 2002/ Returned for modification 30 December 2002/ Accepted 14 January 2003
| ABSTRACT |
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T lymphocytes augments the T helper cell 2 type humoral response but does not alter disease susceptibility. Arthropod transmission of Borrelia burgdorferi spirochetes results in similar antibody isotypes when 
T cells are present, suggesting that vector effects can negate 
T-cell functions in vivo. | TEXT |
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T lymphocytes among the responding immune cells. 
T cells have been shown to influence the T helper (Th) cell response and alter resistance to disease due to intracellular pathogens (10, 11, 13, 16-18), but their effects on the immune response to a vector-borne extracellular pathogen are unknown. We therefore used mice that had been rendered deficient in 
T cells either by antibody (Ab) depletion (BALB/c mice) or by targeted disruption of the T-cell receptor (TCR)
gene (B6.129 TCR
-/- mice [B6.129P2-Tcrdtm1Mom; Jackson Laboratories, Bar Harbor, Maine] and BALB/c TCR
-/- mice [29], a gift of Mark Shlomchik, Yale University) to examine the consequences of 
T-cell deficiency on the course of murine Lyme borreliosis. For Ab depletion, 150 µg of purified hamster anti-mouse 
TCR monoclonal Ab UC7-13D5 or 150 µl of hamster serum was subcutaneously injected into 4- to 5-week-old BALB/c mice daily, beginning 5 days prior to experimental infection and continuing for a total of 9 days.
Mice were infected by either intradermal inoculation of 104 cloned N40 spirochetes in 100 µl of Barbour Stoenner Kelly medium (1) or by infestation with five N40-infected Ixodes scapularis nymphs (5). Fourteen days after infection, lymph node cells from 
T-cell-deficient BALB/c mice produced less gamma interferon (IFN-
) than controls, as measured by cytokine-specific enzyme-linked immunosorbent assay (ELISA) (Fig. 1). Interleukin 4 was detected in culture supernatants of stimulated lymph node cells, consistent with the known Th2 dominance of BALB/c mice (4, 19), and the level was modestly increased in the absence of 
T cells (273 versus 408 pg/ml; P < 0.07). A more dramatic reduction in IFN-
production was noted for B6.129 TCR
-/- mice (Fig. 1), but no interleukin 4 was detected. Thus, the absence of 
T cells in B. burgdorferi infection reduces the Th1 cytokine response, consistent with previous studies showing that 
T cells can direct polarization of
ß Th-cell subsets (11, 17, 18).
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(Table 1). BALB/c TCR
-/- mice had a significant rise in endpoint titers of IgG1 (P = 0.0317, Mann- Whitney test) and tended to have lower IgG2a levels. In contrast, B6.129 TCR
-/- mice exhibited a marked reduction in IgG3 endpoint titers (P = 0.0159, Mann-Whitney test), and titers of IgG2b trended higher. One explanation for the different IgG isotypes induced in the two mouse strains is that 
T cells serve to decrease the genetically dominant Th2 response in BALB/c mice, whereas they promote a Th1 response in B6.129 mice.
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production and downregulation of a Th1-type response by mitogen-stimulated splenocytes (23, 28). Interestingly, in our study, B. burgdorferi-specific IgG isotypes induced in control mice by vector-borne infection paralleled those seen in TCR
-/- mice infected with cultured spirochetes, supporting a vector-induced bias toward Th2 cytokine patterns. Tick-transmitted spirochetes elicited predominantly IgG1 in wild-type BALB/c mice, at levels comparable to those achieved in BALB/c TCR
-/- infected with cultured spirochetes (Table 1). The absence of 
T cells did not lead to a further increase in this Ab subset after vector-borne infection.
Despite the altered cytokine and humoral immune responses in B. burgdorferi-infected 
T-cell-deficient mice, we observed no difference in the severity or prevalence of disease as assessed by histopathology (3). When examined using TCR
-/- mice on two backgrounds or after depletion of 
T cells by monoclonal Ab treatment, no significant differences were noted in arthritis or carditis (Table 2). The relative decrease in B. burgdorferi-specific Th1 responses in TCR
-/- mice did not lead to protracted episodes of carditis even though CD4+ Th1 cells have been shown to promote resolution of this disease manifestation (6). Two previous studies also failed to show an effect of absence of the Th1 cytokine IFN-
on murine Lyme arthritis (8, 14). Mean pathogen burden among mouse groups was the same as assessed by quantitative PCR of the spirochete ospA gene in urinary bladders (data not shown).
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-/- mice were able to develop protective Ab. Both wild-type and TCR
-/- mice that were passively immunized with 500 µl of 1:5 dilution of immune serum from 45-day-infected TCR
-/- mice 24 h prior to challenge infection with tick-borne spirochetes were completely protected as assessed by culture and histopathology (data not shown) (3). This was an expected outcome, because for B. burgdorferi infection, protective and arthritis-resolving antibodies arise in the absence of T-cell help (12, 20).
In summary, we used the murine model of Lyme borreliosis to investigate the effect of 
T cells on the adaptive immune response to a vector-borne extracellular pathogen. While disease expression was not altered, our results show that 
T cells influence the quality of the humoral immune response to B. burgdorferi introduced through the skin and suggest that tick transmission of spirochetes negates the 
T-cell effect. 
T-cell effector functions have been implicated in a variety of inflammatory and infectious processes (9, 15), yet the degree to which these cells play a part in the host immune response remains uncertain. In mammals, the location of these cells at sites of anatomic barriers to the environment suggests a primary role in the early immune response against agents, including arthropod vectors, which can penetrate the barrier. Given the similarity between IgG isotypes induced by vector-borne infection in wild-type mice to those of TCR
-/- mice, it is possible that the Th cell bias attributed to tick saliva may be due to its actions on dendritic epidermal 
T cells. These cells may contribute to the local cytokine milieu for maturing dendritic cells in the skin and influence the priming of
/ß T-cell responses in the lymph nodes. Although 
T-cell effects do not alter the outcome from B. burgdorferi infection, our results have important implications for other vector-borne pathogens transmitted through the skin.
| ACKNOWLEDGMENTS |
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This work was supported by NIH AR42637, AI50604, and AR47058 and the Arthritis Foundation (L.K.B.) and NIH AI26815 (S.W.B.).
| FOOTNOTES |
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