Characterization of T and B cells isolated from mucosa-associated tissues of the rhesus macaque

Maintenance of caecal homeostasis by diverse adaptive immune cells in the rhesus macaque

Objectives

The caecum bridges the small and large intestine and plays a front-line role in discriminating gastrointestinal antigens. Although dysregulated in acute and chronic conditions, the tissue is often overlooked immunologically.

Methods

To address this issue, we applied single-cell transcriptomic-V(D)J sequencing to FACS-isolated CD45+ caecal patch/lamina propria leukocytes from a healthy (5-year-old) female rhesus macaque ex vivo and coupled these data to VDJ deep sequencing reads from haematopoietic tissues.

Results

We found caecal NK cells and ILC3s to co-exist with a spectrum of effector T cells partially derived from SOX4 + recent thymic emigrants. Tolerogenic Vγ8Vδ1-T cells, plastic CD4+ T helper cells and GZMK + EOMES + and TMIGD2 + tissue-resident memory CD8+ T cells were present and differed metabolically. An IL13 + GATA3 + Th2 subset expressing eicosanoid pathway enzymes was accompanied by IL1RL1 + GATA3 + regulatory T cells and a minor proportion of IgE+ plasma cells (PCs), illustrating tightly regulated type 2 immunity devoid of ILC2s. In terms of B lymphocyte lineages, caecal patch antigen-presenting memory B cells sat alongside germinal centre cells undergoing somatic hypermutation and differentiation into IGF1 + PCs. Prototypic gene expression signatures decreased across PC clusters, and notably, expanded IgA clonotypes could be traced in VDJ deep sequencing reads from additional compartments, including the bone marrow, supporting that these cells contribute a steady stream of systemic antibodies.

Conclusions

The data advance our understanding of caecal immunological function, revealing processes involved in barrier maintenance and molecular networks relevant to disease.

Characterization of New Zealand White Rabbit Gut-Associated Lymphoid Tissues and Use as Viral Oncology Animal Model

Rabbits have served as a valuable animal model for the pathogenesis of various human diseases, including those related to agents that gain entry through the gastrointestinal tract such as human T cell leukemia virus type 1. However, limited information is available regarding the spatial distribution and phenotypic characterization of major rabbit leukocyte populations in mucosa-associated lymphoid tissues. Herein, we describe the spatial distribution and phenotypic characterization of leukocytes from gut-associated lymphoid tissues (GALT) from 12-week-old New Zealand White rabbits. Our data indicate that rabbits have similar distribution of leukocyte subsets as humans, both in the GALT inductive and effector sites and in mesenteric lymph nodes, spleen, and peripheral blood. GALT inductive sites, including appendix, cecal tonsil, Peyer's patches, and ileocecal plaque, had variable B cell/T cell ratios (ranging from 4.0 to 0.8) with a predominance of CD4 T cells within the T cell population in all four tissues. Intraepithelial and lamina propria compartments contained mostly T cells, with CD4 T cells predominating in the lamina propria compartment and CD8 T cells predominating in the intraepithelial compartment. Mesenteric lymph node, peripheral blood, and splenic samples contained approximately equal percentages of B cells and T cells, with a high proportion of CD4 T cells compared with CD8 T cells. Collectively, our data indicate that New Zealand White rabbits are comparable with humans throughout their GALT and support future studies that use the rabbit model to study human gut-associated disease or infectious agents that gain entry by the oral route.

Characterization of Anti-Gal Antibody-Producing Cells of Baboons and Humans

BACKGROUND

Anti-Gal antibodies cause hyperacute and delayed xenograft rejection in pig-to-primate transplantation. The cell populations producing anti-Gal and other natural antibodies in primates are unknown.

METHODS

Cells from different lymphoid compartments of naïve or sensitized baboons were examined for anti-Gal and total Ig production by ELISPOT. B and plasma cells from humans and baboons were purified by FACS sorting and characterized for anti-Gal and total Ig production and cytology.

RESULTS

In naïve baboons, the spleen was the major source of anti-Gal IgM-secreting cells. Two months after sensitization with porcine tissues, high frequencies of anti-Gal IgM- and IgG-secreting cells were detected in the spleen, lymph nodes, and bone marrow. Six months after antigen exposure, anti-Gal IgM- and IgG-secreting cells were preferentially localized in the bone marrow. Cells from human spleen, bone marrow, and blood were also analyzed and anti-Gal IgM-secreting cells were detected mainly in the spleen. Sorting of baboon and human cells showed that anti-Gal IgM-secreting cells were mainly splenic B cells (CD20+, CD138-, and Ig+). Although low in percentage, sorted CD20-CD138+ plasma cells in spleen and bone marrow secreted large quantities of anti-Gal IgM. Most anti-Gal IgG-secreting cells were plasma cells (CD138+) at both early (Ig+) and late (Ig-) stages of differentiation.

CONCLUSIONS

Similar to Gal knockout mice, natural anti-Gal IgM antibodies in primates are produced mainly by splenic B cells. After antigen exposure, anti-Gal IgM and IgG were secreted by both B and plasma cells. These results suggest strategies to remove xenoreactive antibody-secreting cells prior to transplantation.

Female sex hormones as regulatory factors in the vaginal immune compartment

Sexually transmitted diseases (STD) are now considered to be among the most common human infections. The incidence of STD is on the rise, which is partly due to frequent transmission during the asymptomatic phase of infection. The compounded cost of STD just in the United States is estimated to exceed $10 billion annually. STD are particularly prevalent in teenagers and young adults and the health problems caused by these diseases tend to be more severe and more frequent in woman than in men. Despite considerable efforts, a vaccine that provides protective immunity against sexually transmitted diseases in humans has not been developed. Nonetheless, research in animal models indicates that strong local and regional immune responses can influence the outcome of vaginal challenge with microbial pathogens. Vaginal immunity is an area of basic immunology that has received relatively little attention, but it is already clear that the mucosal and regional immunology of the vagina has unique features. The present review summarizes some of the anatomical, physiological and immunological features of the vagina and uterus that distinguish humans, non-human primates, rats and mice. These interspecies differences need to be taken into account in laboratory efforts to develop effective vaccines for STD in humans.

Aging impairs intestinal immunity

The elderly are characterized by immunosenescence accompanied by high rates of morbidity and mortality associated with infectious diseases. Despite suggestions that the mucosal immune compartment is relatively unaffected by aging, there are marked deficits in the intestinal mucosal immune responses of old animals and elderly humans. Little is known about the mechanism(s) whereby aging disrupts intestinal immunity. However, several events in the genesis of the intestinal immune response may be perturbed during aging. The first step is the uptake of antigens by specialized epithelial cells (M cells) that overlie the domes of Peyer's patches. We are unaware of any studies on the efficacy of antigen uptake in the intestine as a function of age. The effects of aging on the next step, antigen presentation by dendritic cells and lymphocyte isotype switching, have not been resolved. The third event is the maturation of immunoglobulin A (IgA) immunoblasts and their migration from the Peyer's patches to the intestinal mucosa. Quantitative immunohistochemical analyses suggest that the migration of these putative plasma cells to the intestinal effector site is compromised in old animals. Local antibody production by mature IgA plasma cells in the intestinal mucosa constitutes the fourth step. We recently reported that in vitro IgA antibody secretion by intestinal lamina propria lymphocytes from young and senescent rats is equivalent. The last event is the transport of IgA antibodies across the epithelial cells via receptor-mediated vesicular translocation onto the mucosal surface of the intestine. Receptor-binding assays did not detect age-associated declines in receptor number or binding affinity in either rodent or primate enterocytes as a function of donor age. Efforts to identify the mechanism(s) responsible for the age-related decline in intestinal mucosal immune responsiveness may benefit by focusing on the homing of IgA immunoblasts to the effector site.

Systemic and intestinal immune responses to HIV-2287 infection in Macaca nemestrina

Nonhuman primate models of human AIDS have been used successfully to evaluate candidate vaccines and infection intervention therapies. Successes of pathogenicity studies in primate models have been limited because of the varied infection outcomes and characteristic low number of study animals. The acutely pathogenic HIV-2(287)--Macaca nemestrina model has shown promise both in antiviral drug evaluation and in pathogenicity studies. Here we describe virus replication, spread, and host responses during the first 28 days of HIV-2(287) infection. Focusing on 18 macaques from a larger 27-macaque study, we report changing virus loads, CD4(+) cell depletions, and antibody responses both systemically and in the mucosa of the small intestine. After intravenous inoculation, blood and intestinal tissue were collected from pairs of macaques at 12 hr and 1, 2, 4, 6, 10, 14, 21, and 28 days postinfection. Specimens were examined for evidence of infection by quantitative cultures, in situ hybridization, lymphocyte subset monitoring, and antibody production. The data were presented serially as though all samples were collected from a single macaque. The highest blood virus loads were detected between days 10 and 14 and subsequently decreased through day 28. This coincided with a significant increase in ileum mucosa virus loads on day 10, which became undetectable by day 28. The lowest levels of CD4(+) cells were observed on days 21 and 28 in blood and ileum mucosa. CD4(+):CD8(+) cell ratios in blood and ileum dropped dramatically after day 10 to lowest levels by day 28. Intestinal virus loads were inversely correlated with CD4(+) cell and virus-specific antibody levels in the ileum after day 6. These results underscore the suitability of this model for pathogenicity studies as well as the importance of the intestinal lymphoid tissues as an initial site of virus replication and cell destruction during the acute, asymptomatic stage of AIDS development.

Selective Induction of Protective MHC Class I-Restricted CTL in the Intestinal Lamina Propria of Rhesus Monkeys by Transient SIV Infection of the Colonic Mucosa

The identification of mucosal immune responses required for protection against sexual transmission of HIV is essential for the development of an efficacious vaccine. To gain a better understanding of these responses, we have characterized the immune responses in the lamina propria (LP) and epithelium of the jejunum, the mesenteric lymph nodes, and peripheral blood (PBMC) of 11 rhesus monkeys following colonic exposure to two molecular clones of SIV. Two monkeys had no signs of infection. Three monkeys became persistently infected. Transient infections, characterized by the sporadic detection of virus in the periphery and/or detection of SIV-specific immune responses in either the gut-associated tissues or PBMC, were induced in six of the monkeys. One persistently infected and three transiently infected monkeys had high levels of SIV env-specific MHC class I restricted CTL in the jejunal LP. Another transiently infected monkey had SIV-specific IgA secreting B cells in the LP. Three or six months postexposure, these animals and four naive controls were challenged intracolonically with the heterologous primary isolate, SIV/DeltaB670. All four monkeys with strong SIV env-specific MHC-restricted CTL in the LP were protected, whereas none of the naive controls or the remaining seven monkeys with little or no CTL in the LP were protected. These experiments provide the first direct evidence that transient mucosal infection can induce SIV-specific immunity that remains localized to the gut-associated tissues. Furthermore, a strong correlation between SIV env-specific MHC-restricted CTL in the LP and protection against colonic mucosal challenge was observed.

Characterization of gut-associated lymphoid tissue (GALT) of normal rhesus macaques

This study characterizes the gut-associated lymphoid tissue (GALT) of normal healthy rhesus macaques and compares the percentages of T and B cell subsets to those of systemic lymphoid tissue. Lymphocytes from the systemic lymphoid tissue (spleen, axillary, and inguinal lymph nodes), mesenteric lymph nodes (MLN), and intestinal epithelium (IEL) and lamina propria (LPL) of the jejunum, ileum, and colon were examined from both adult and juvenile, normal rhesus macaques. Lymphocytes were analyzed for expression of CD2, CD3, CD4, CD8, CD25, gamma delta TCR, and CD20 by two- or three-color flow cytometric analysis. Sections of jejunum, ileum, and colon were examined for CD3, CD20, and CD103 expression by immunohistochemistry. Peyer's patches were also examined for CD3, CD4, CD8, and CD20 expression by immunohistochemistry. Most IEL and LPL were CD103+, CD3+ T cells with significantly fewer CD20+ B cells. The IEL were predominantly CD3+CD8+ (63-80%), with very few CD4+ cells, whereas CD4:CD8 ratios in the LPL ranged from 0.74 to 1.3. Three to 38% of the IEL were gamma delta TCR positive, but gamma delta expression was rare in the LPL and MLN. gamma delta TCR expression was also higher in the IEL of younger animals. LPL had higher expression of CD25 compared to IEL and systemic tissues, particularly in aged animals. CD4+CD8+, double-positive and CD3+CD4-CD8- double-negative cells were also observed in GALT. These results demonstrate that GALT of rhesus macaques is remarkably similar to that of humans, further justifying the use of these animals as models for various intestinal disorders.

Psychological disturbance differentially alters CD4+ and CD8+ leukocytes in the blood and intrathecal compartments

To evaluate cellular changes in the intrathecal compartment in response to psychological stress, cerebrospinal fluid (CSF) and peripheral blood (PB) samples were obtained from rhesus monkeys under baseline and challenge conditions. Juvenile monkeys separated from their social companions overnight had elevated cortisol, increased polymorphonuclear (PMN), and fewer CD4+ and CD8+ leukocytes in PB. In contrast, in CSF there were more CD4+ and fewer CD8+ leukocytes, raising the CD4/CD8 ratio. Dexamethasone given intramuscularly caused similar hematological changes; i.e. neutrophilia and lymphocytopenia with fewer CD4+ and CD8+ leukocytes in PB. However, it did not induce similar changes in CSF, indicating that the stress-related shift of CD4+ leukocytes in the intrathecal compartment involves physiological processes beyond adrenocortical steroids.

Impact of aging on gastrointestinal mucosal immunity

There is considerable evidence that the mucosal or secretory immune response in the gastrointestinal tract is compromised by aging. The generation of a mucosal immune response is an extremely complex process that involves antigenic stimulation of a specific subpopulation of immunologically competent cells in the Peyer's patches, differentiation and migration of these cells to the small intestinal lamina propria, initiation and regulation of local antibody production in the intestinal wall, and mucosal epithelial cell receptor-mediated transport of antibodies to the intestinal lumen. Available data suggest that gastrointestinal mucosal immunosenescence reflects deficits in: (1) the differentiation and/or migration (homing) of immunoglobulin A immunoblasts to the intestinal lamina propria, and (2) the initiation and/or regulation of local antibody production. The significant age-related increases in the incidence and severity of gastrointestinal infectious diseases, coupled with the potential for immunopharmacologic manipulation of the mucosal immune compartment, substantiate the merit of studies designed to resolve the etiology of mucosal immunodeficiency in the elderly.

Leukocyte trafficking in free-flowing cerebrospinal fluid of normal rhesus macaques (Macaca mulatta)

Cellular components in free-flowing cerebrospinal fluid (CSF) of normal rhesus macaques were characterized. Microscopic counting enumerated the total number of leukocytes, percentage of polymorphonuclear cells (PMN), leukocytes with nonspecific esterase (NSE), and those reducing nitro blue tetrazolium (NBT). Flow cytometric analysis further identified CD4, CD8, CD14, and CD20 positive leukocytes. These experiments established reliable techniques for evaluating cellular components in CSF from rhesus macaques and documented the difference in the CD4/CD8 ratio between peripheral blood (PB) and CSF compartments under normal physiological conditions.