T helper responsiveness in human Loa loa infection; defective specific proliferation and cytokine production by CD4+ T cells from microfilaraemic subjects compared with amicrofilaraemics

Abstract

SUMMARYThe proliferation and cytokine profiles of peripheral blood mononuclear cells (PBMC) from microfilaraemic (Mf þ ) subjects infected by Loa loa in response to antigens of several parasitic stages were compared with those from amicrofilaraemic (Mf ¹ ) individuals. While a strong lymphoproliferative response and consistent levels of both Th1 (IL-2, interferon-gamma (IFN-g)) and Th2 (IL-4, IL-5) type cytokines were observed in response to adult worm (AW) and microfilariae (Mf) antigen in Mf ¹ individuals, Mf þ subjects were characterized by a T cell unresponsiveness, including proliferation, cytokine production and IL-2 mRNA expression. Conversely, T cell responsiveness to mitogens and non-specific antigen were similar in the two endemic populations. Depletion of lymphocyte subpopulations indicated that T CD4 þ were mainly involved in the specific cellular response. In contrast to other cytokines, IL-10 was produced in response to all parasitic stages, in both Mf þ and Mf ¹ patients. Neutralization of IL-10 did not restore cytokine production in Mf þ patients, while B7 mRNA expression was similar between Mf þ and Mf ¹ subjects in response to Mf antigen, suggesting that IL-10 was not the only factor responsible for T cell unresponsiveness. Mf þ patients have lower Mf antigen-specific IgG levels compared with Mf ¹ , and there is a significant correlation between Mf antigen-specific antibodies and IL-5 responses. These findings suggest that Mf ¹ status is correlated with T helper responsiveness, including proliferation and production of both Th1-and Th2-type cytokines, whereas Mf þ status is characterized by unresponsiveness of the same cell population, induced and/or maintained by microfilariae.

Increased frequency of Th2-type cytokine-producing T cells in microfilaremic loiasis.

“…12 In human loiasis, however, the same research group described significantly higher IL-10 production in amicrofilaremic than in microfilaremic subjects and concluded that this cytokine is not responsible for the Th unresponsiveness observed in the microfilaremic group. 14 The apparent divergences concerning the contribution of IL-10 to microfilaria-specific hyporesponsiveness can not be fully resolved by our data because we concentrated on analyses of cytokine production and T cell subpopulations and did not perform lymphoproliferation assays. In all, the expansion of the IL-10-producing lymphocyte subpopulation in our microfilaremic subjects did not significantly influence the frequency of Th1 cytokine-expressing cells represented by intracellular staining of IFN-␥, IL-2, and IFN-␥/IL-2.…”

“…18 This finding has recently been substantiated in a study of human loiasis, which showed no differences between microfilaremic and amicrofilaremic individuals with respect to lymphoproliferation and cytokine production when PBMC were stimulated with nonspecific mitogens. 14 In addition, in a longitudinal study of L. loa-infected rhesus monkeys, blastogenic responses of PBMC and IL-2 production capacity decreased only after stimulation with filarial antigen. 13 By applying nonspecific (non-filarial) stimulants in our flow cytometric assay, it was nevertheless possible to elaborate differences between microfilaremic loiasis and the amicrofilaremic group, with an expansion of IL-4-, IL-10-, and IL-13-expressing CD4 ϩ cells within the microfilaremic individuals.…”

“…10,11 Most recent data concerning the cytokine profile in loiasis are derived from mandrills and rhesus monkeys experimentally infected with L. loa and from one study of immune responsiveness in human loiasis. [12][13][14] These studies appear suitable for illustrating some aspects of the infection; However, the lack of a detailed analysis of cytokine-producing T cells in human loiasis is still evident.…”

Transmission Intensity Affects Both Antigen-Specific and Nonspecific T-Cell Proliferative Responses inLoa loaInfection

“…or phytohemagglutinin (PHA; 10 g/ml; Sepracor, Villeneuve-la-Garenne, France) as mitogen. For Ag, cells were stimulated with Mycobacterium tuberculosis purified protein derivative (PPD; 10 g/ ml, Statens Serum Institut, Copenhagen, Denmark), the parasite Ag L3 (2 g/ ml), adult worm (5 g/ml), or Mf Ag (10 g/ml), or medium alone, exactly as described previously (3). The plates were incubated at 37°C under an atmosphere of 5% CO 2 -air for 3 days (mitogen) or 5 days (Ag) and then pulsed with 1 Ci of [ 3 H]thymidine/well (Amersham, Les Ulis, France).…”

“…Culture supernatants were collected at 24 h (mitogens) and 48 h (Ag) for IL-2 and IL-4 determinations and at 96 h (antigens) for measurement of IL-5 and IFN-␥. Cytokine levels were measured by two-site enzyme-linked immunosorbent assay exactly as described previously (3). Results for IL-4 and IL-5 are expressed in picograms per milliliter and results for IL-2 are in units per milliliter, relative to human cytokine standards (R & D Systems, Abingdon, United Kingdom).…”