Parul Tripathi

Immunostimulatory cellular responses of cured Leishmania -infected patients and hamsters against the integral membrane proteins and non-membranous soluble proteins of a recent clinical isolate of Leishmania donovani

Development of an effective immunoprophylactic agent for visceral leishmaniasis (VL) has become imperative due to the increasing number of cases of drug resistance and relapse. Live and killed whole parasites as well as fractionated and recombinant preparations have been evaluated for vaccine potential. However, a successful vaccine against the disease has been elusive. Because protective immunity in human and experimental leishmaniasis is predominantly of the Th1 type, immunogens with Th1 stimulatory potential would make good vaccine candidates. In the present study, the integral membrane proteins (IMPs) and non‐membranous soluble proteins (NSPs), purified from promastigotes of a recent field isolate, Leishmania donovani stain 2001, were evaluated for their ability to induce cellular responses in cured patients (n = 9), endemic controls (n = 5) of visceral leishmaniasis (VL) and treated hamsters (n = 10). IMPs and NSPs induced significant proliferative responses (SI 6·3 ± 4·1 and 5·6 ± 2·3, respectively; P < 0·01) and IFN‐γ production (356·3 ± 213·4 and 294·29 ± 107·6 pg/ml, respectively) in lymphocytes isolated from cured VL patients. Significant lymphoproliferative responses against IMPs and NSPs were also noticed in cured Leishmania animals (SI 7·2 ± 4·7 & 6·4 ± 4·1, respectively; P < 0·01). In addition, significant NO production in response both IMPs and NSPs was also noticed in macrophages of hamsters and different cell lines (J774A‐1 and THP1). These results suggest that protective, immunostimulatory molecules are present in the IMP and NSP fractions, which may be exploited for development of a subunit vaccine for VL.

Innate and specific gut-associated immunity and microbial interference.

Certain bacterial species isolated from the gastrointestinal microbial communities release low-molecular-weight peptides into milk products using bacteria-derived proteases that degrade milk casein, and thereby generate peptides, triggering immune responses. The intestinal microbial communities contributes to the processing of food antigens in the gut. The present study was designed to investigate the immunomodulatory effects of microbial interference to determine whether casein degraded by probiotic bacteria-derived enzymes could modulate the cytokine production and peripheral blood mononuclear cells in atopic infants with cow or other synthetic milk allergy. Without hydrolyzation, casein reduced the production of interleukin-4, which indicates that probiotics modify the structure of potentially harmful antigens and thereby alter the mode of their immunogenicity. Intraluminal bacterial antigens have been reported to elicit specific responses in the gut-associated lymphoid tissue (GALT) through the binding capacity of intraluminal bacterial antigens to epithelial cells, which allows antigen entry via enterocytes and aids in evading the tolerance function in Peyers patches. Such tonic immune responses in the GALT may allow control of the metabolic activity and balance of the gut microbial communities.

Identification of Leishmania donovani antigens stimulating cellular immune responses in exposed immune individuals

Human visceral leishmaniasis (VL), also known as kala azar (KA) in India, is a systemic progressive disease caused by Leishmania donovani. In VL, Th1 responses correlate with recovery from and resistance to disease and resolution of infection results in lifelong immunity against the disease. However, recent data suggest an important role for interleukin (IL)‐10 in maintaining the resistant state. We evaluated whole cell extract (WE) and 11 antigenic fractions [F1–F11, molecular weight (MW) range of 139–24·2 kDa] from L. donovani (2001 strain, a fresh field isolate from Bihar), for their ability to induce in vitro T cell proliferation and production of interferon (IFN)‐γ, interleukin (IL)‐12, IL‐10 and IL‐4 by peripheral blood mononuclear cells (PBMCs) of exposed immune individuals (14 patients with history of VL, 10 household endemic contacts) and 20 non‐endemic healthy controls. Twenty‐one of 24 exposed individuals and no healthy controls showed proliferative response to WE. Whole‐extract activated IFN‐γ, IL‐12, IL‐10 levels were higher in the exposed group than in controls; IL‐4 was not detectable in any of the samples. Among 21 responders to WE, frequent proliferative responses were seen to fractions F1–F4 (MW > 64·2 kDa) and none to fractions F5–F11; fractions F1–F11 stimulated comparable levels of IFN‐γ and IL‐12 while IL‐10 levels were higher in response to F5–F11 compared to F1–F4. These data demonstrate the presence of immunostimulatory antigens in the high MW fractions of whole L. donovani antigen. However, these fractions do not stimulate a Th1 response and produce variable amounts of IFN‐γ and the regulatory cytokine, IL‐10. Hence, these high MW immunostimulatory fractions need to be evaluated in greater depth for their possible role as protective antigens.