Differential expression of adhesion molecules and chemokines between nasal and small intestinal mucosae: implications for T- and sIgA+ B-lymphocyte recruitment

The natural history of COVID-19 in vaccinated inflammatory bowel disease patients

AIM

Assess the characteristics of break through COVID-19 in Inflammatory Bowel Disease (IBD) patients, despite complete vaccination.

METHODS

Patients who reported a COVID-19 at least 3 weeks after complete vaccination were asked to answer an on-line anonymous questionnaire which included patient and disease characteristics, vaccination history, and the evolution of COVID-19.

RESULTS

Among 3240 IBD patients who reported complete vaccination between 1st May 2021 and 30thJune 2022, 402 (12.4%) were infected by SARS Cov-2 [223 male, 216 Crohn's disease (CD), 186 Ulcerative Colitis (UC), mean (SD) age 42.3 (14.9) years, mean (SD) IBD duration 10.1 (9.7) years]. Three hundred and sixty-nine patients (91.8%) were infected once and 33 (8.2%) twice. The mean (SD) time between last vaccination and infection was 4.1 (1.6) months. Overall, 351 (87.3%) patients reported mild constitutional and/or respiratory symptoms, 34 (8.4%) were asymptomatic and only 17 patients (4.2%) required hospitalization. Of hospitalized patients, 2 UC patients died of COVID-19 pneumonia. The remaining hospitalized patients did not need high flow oxygen supply or ICU admission.

CONCLUSIONS

A minority of completely vaccinated IBD patients developed COVID-19 which evolved with mild symptoms and a favorable outcome. These results reinforce the importance of vaccination especially in vulnerable populations.

Antibody decay, T cell immunity and breakthrough infections following two SARS-CoV-2 vaccine doses in inflammatory bowel disease patients treated with infliximab and vedolizumab

Anti tumour necrosis factor (anti-TNF) drugs increase the risk of serious respiratory infection and impair protective immunity following pneumococcal and influenza vaccination. Here we report SARS-CoV-2 vaccine-induced immune responses and breakthrough infections in patients with inflammatory bowel disease, who are treated either with the anti-TNF antibody, infliximab, or with vedolizumab targeting a gut-specific anti-integrin that does not impair systemic immunity. Geometric mean [SD] anti-S RBD antibody concentrations are lower and half-lives shorter in patients treated with infliximab than vedolizumab, following two doses of BNT162b2 (566.7 U/mL [6.2] vs 4555.3 U/mL [5.4], p <0.0001; 26.8 days [95% CI 26.2 - 27.5] vs 47.6 days [45.5 - 49.8], p <0.0001); similar results are also observed with ChAdOx1 nCoV-19 vaccination (184.7 U/mL [5.0] vs 784.0 U/mL [3.5], p <0.0001; 35.9 days [34.9 - 36.8] vs 58.0 days [55.0 - 61.3], p value < 0.0001). One fifth of patients fail to mount a T cell response in both treatment groups. Breakthrough SARS-CoV-2 infections are more frequent (5.8% (201/3441) vs 3.9% (66/1682), p = 0.0039) in patients treated with infliximab than vedolizumab, and the risk of breakthrough SARS-CoV-2 infection is predicted by peak anti-S RBD antibody concentration after two vaccine doses. Irrespective of the treatments, higher, more sustained antibody levels are observed in patients with a history of SARS-CoV-2 infection prior to vaccination. Our results thus suggest that adapted vaccination schedules may be required to induce immunity in at-risk, anti-TNF-treated patients.

Risk factors for SARS-CoV-2 infection and course of COVID-19 disease in patients with IBD in the Veterans Affair Healthcare System

OBJECTIVE

Our aim was to explore the risk of infection with all classes of inflammatory bowel disease (IBD) medications and the impact of these medications on the disease course in a nationwide cohort of patients with IBD.

DESIGN

This was a retrospective national cohort study of patients with IBD in the Veterans Affairs Healthcare System. We categorised IBD medication use immediately prior to the COVID-19 pandemic and used survival analysis methods to study associations with SARS-CoV-2 infection, as well as a combined secondary outcome of COVID-19 hospitalisation or COVID-19-related mortality.

RESULTS

The analytical cohort of 30 911 patients was primarily male (90.9%), white (78.6%) and with ulcerative colitis (58.8%). Over a median follow-up of 10.7 months, 649 patients (2.1%) were diagnosed with SARS-CoV-2 infection and 149 (0.5%) met the combined secondary outcome. In adjusted models, vedolizumab (VDZ) use was significantly associated with infection relative to mesalazine alone (HR 1.70, 95% CI 1.16 to 2.48, p=0.006). Patients on no IBD medications had increased risk of the combined secondary outcome relative to mesalazine alone (sub-HR 1.64, 95% CI 1.12 to 2.42, p=0.01), however, no other IBD medication categories were significantly associated with this outcome, relative to mesalazine alone (each p>0.05). Corticosteroid use was independently associated with both SARS-CoV-2 infection (HR 1.60, 95% CI 1.23 to 2.09, p=0.001) and the combined secondary outcome (sub-HR 1.90, 95% CI 1.14 to 3.17, p=0.01).

CONCLUSION

VDZ and corticosteroid were associated with an increased risk of SARS-CoV-2 infection. Except for corticosteroids no medications including mesalazine were associated with an increased risk of severe COVID-19.

Review article: prevention, diagnosis and management of COVID-19 in the IBD patient

BACKGROUND

The current COVID-19 pandemic, caused by SARS-CoV-2, has emerged as a public health emergency. All nations are seriously challenged as the virus spreads rapidly across the globe with no regard for borders. The primary management of IBD involves treating uncontrolled inflammation with most patients requiring immune-based therapies. However, these therapies may weaken the immune system and potentially place IBD patients at increased risk of infections and infectious complications including those from COVID-19.

AIM

To summarise the scale of the COVID-19 pandemic, review unique concerns regarding IBD management and infection risk during the pandemic and assess COVID-19 management options and drug interactions in the IBD population.

METHODS

A literature review on IBD, SARS-CoV-2 and COVID-19 was undertaken and relevant literature was summarised and critically examined.

RESULTS

IBD patients do not appear to be more susceptible to SARS-CoV-2 infection and there is no evidence of an association between IBD therapies and increased risk of COVID-19. IBD medication adherence should be encouraged to prevent disease flare but where possible high-dose systemic corticosteroids should be avoided. Patients should exercise social distancing, optimise co-morbidities and be up to date with influenza and pneumococcal vaccines. If a patient develops COVID-19, immune suppressing medications should be withheld until infection resolution and if trial medications for COVID-19 are being considered, potential drug interactions should be checked.

CONCLUSIONS

IBD patient management presents a challenge in the current COVID-19 pandemic. The primary focus should remain on keeping bowel inflammation controlled and encouraging medication adherence.

CCL28 Is Involved in Mucosal IgA Responses, Olfaction, and Resistance to Enteric Infections

CCL28 is a mucosal chemokine that has been involved in various responses, including IgA production. We have analyzed its production in human tissues using a comprehensive microarray database. Its highest expression is in the salivary gland, indicating that it is an important component of saliva. It is also expressed in the trachea, bronchus, and in the mammary gland upon onset of lactation. We have also characterized a Ccl28-/- mouse that exhibits very low IgA levels in milk, and the IgA levels in feces are also reduced. These observations confirm a role for the CCL28/CCR10 chemokine axis in the recruitment of IgA plasmablasts to the lactating mammary gland. CCL28 is also expressed in the vomeronasal organ. We also detected olfactory defects (anosmia) in a Ccl28-/- mouse suggesting that CCL28 is involved in the function/development of olfaction. Importantly, Ccl28-/- mice are highly susceptible to Salmonella enterica serovar Typhimurium in an acute model of infection, indicating that CCL28 plays a major role in innate immunity against Salmonella in the gut. Finally, microbiome studies revealed modest differences in the gut microbiota between Ccl28-/- mice and their cohoused wild-type littermates. The latter observation suggests that under homeostatic conditions, CCL28 plays a limited role in shaping the gut microbiome.

Lactogenic immunity and vaccines for porcine epidemic diarrhea virus (PEDV): Historical and current concepts

Morbidity, mortality, and loss of productivity from enteric diseases in neonatal piglets cost swine producers millions of dollars annually. In 2013-2014, the porcine epidemic diarrhea virus (PEDV) outbreak led to $900 million to $1.8 billion in annual losses to US swine producers. Passive lactogenic immunity remains the most promising and effective way to protect neonatal suckling piglets from enteric diseases like PEDV. Protecting suckling piglets through lactogenic immunity is dependent on trafficking of pathogen-specific IgA plasmablasts to the mammary gland and accumulation of secretory IgA (sIgA) antibodies in milk, defined as the gut-mammary-sIgA axis. Due to an impermeable placenta, piglets are born agammaglobulinic, and are highly susceptible to a plethora of infectious agents. They rely solely on colostrum and milk antibodies for maternal lactogenic immunity. Previous advances in the development of live and attenuated vaccines for another devastating diarrheal virus of pigs, transmissible gastroenteritis virus (TGEV), provide insights into the mechanisms of maternal immunity and piglet protection. In this chapter, we will review previous research on TGEV-induced lactogenic immunity to provide a historical perspective on current efforts for PEDV control and vaccines in the swine industry. Identifying factors that influence lactogenic immunity and the gut-mammary-sIgA axis may lead to improved vaccine regimens for PEDV and other enteric pathogens in gestating swine and improved overall herd immunity, swine health and industry productivity.

Tissue Microenvironments in the Nasal Epithelium of Rainbow Trout (Oncorhynchus mykiss) Define Two Distinct CD8α+ Cell Populations and Establish Regional Immunity

Mucosal surfaces require balancing different physiological roles and immune functions. To effectively achieve multifunctionality, mucosal epithelia have evolved unique microenvironments that create unique regional immune responses without impairing other normal physiological functions. Whereas examples of regional immunity are known in other mucosal epithelia, to date, no immune microenvironments have been described in the nasal mucosa, a site where the complex functions of olfaction and immunity need to be orchestrated. In this study we identified the presence of CD8α⁺ cells in the rainbow trout (Oncorhynchus mykiss) nasal epithelium. Nasal CD8α⁺ cells display a distinct phenotype suggestive of CD8⁺ T cells with high integrin β₂ expression. Importantly, nasal CD8α⁺ cells are located in clusters at the mucosal tip of each olfactory lamella but scattered in the neuroepithelial region. The grouping of CD8α⁺ cells may be explained by the greater expression of CCL19, ICAM-1, and VCAM-1 in the mucosal tip compared with the neuroepithelium. Whereas viral Ag uptake occurred via both tip and lateral routes, tip-resident MHC class II⁺ cells are located significantly closer to the lumen of the nasal cavity than are their neuroepithelial counterparts, therefore having quicker access to invading pathogens. Our studies reveal compartmentalized mucosal immune responses within the nasal mucosa of a vertebrate species, a strategy that likely optimizes local immune responses while protecting olfactory sensory functions.

Oral antigen exposure in newborn piglets circumvents induction of oral tolerance in response to intraperitoneal vaccination in later life

Background

We previously determined that newborn piglets orally gavaged with Ovalbumin (OVA) responded to systemic OVA re-exposure with tolerance; if adjuvants were included in oral vaccine, piglets responded with antibody-mediated immunity (Vet Immunol Immunopathol 161(3–4):211–21, 2014). Here, we will investigate whether newborn piglets gavaged with a vaccine comprised of OVA plus unmethylated CpG oligodeoxynucleotides (CpG; soluble component; OVA/CpG) combined with OVA plus CpG encapsulated within polyphosphazene microparticles (MP; particulate component) responded with systemic and mucosal immunity. To monitor the response to systemic antigen re-exposure, piglets were i.p.-immunized with OVA plus Incomplete Freund’s Adjuvant (IFA) one month later.

Results

Newborn piglets (n = 5/group) were gavaged with a combined soluble and particulate vaccine consisting of OVA (0.5-0.05 mg) plus 50 μg CpG and 0.5 mg OVA plus 50 μg CpG encapsulated within a polyphosphazene MP (0.5 mg) referred to as OVA/CpG + MP. Control piglets were gavaged with saline alone. Piglets were i.p. immunized with 10 mg OVA (or saline) in IFA at four weeks of age and then euthanized at eight weeks of age. We observed significantly higher titres of serum anti-OVA immunoglobulin (Ig) IgM, IgA, IgG, IgG1, IgG2 and IgG in piglets immunized with 0.05 mg OVA/CpG + MP relative to saline control animals. Thus, a single oral exposure at birth to a combined soluble and particulate OVA vaccine including adjuvants can circumvent induction of oral tolerance which impacts response to i.p. vaccination in later life. Further, piglets gavaged with 0.05 mg OVA/CpG + MP generated significant anti-OVA IgG and IgG1 titres in lung compared to saline control piglets but results were comparable to titres measured in parenteral control piglets. Peripheral blood mononuclear cells (PBMCs) ex vivo-stimulated with OVA showed markedly decreased production of IL-10 cytokine after 72 hours relative to animal-matched cells incubated with media alone. No production of IFN-γ was observed from any groups.

Conclusion

Newborn piglets gavaged with low dose soluble and particulate OVA plus CpG ODN and polyphosphazene adjuvants produced antigen-specific antibodies in serum and lung after systemic re-exposure in later life. These data indicate circumvention of oral tolerance but not induction of oral immunity.

The Mammary Gland in Mucosal and Regional Immunity

The mammary gland (MG) lacks a mucosa but is part of the mucosal immune system because of its role in passive mucosal immunity. The MG is not an inductive site for mucosal immunity. Rather, synthesis of immunoglobulin (Ig)A by plasma cells stimulated at distal inductive sites dominate in the milk of rodents, humans, and swine whereas IgG1 derived from serum predominates in ruminants. Despite the considerable biodiversity in the role of the MG, IgG passively transfers the maternal systemic immunological experience whereas IgA transfers the mucosal immunological experience. Although passive antibodies are protective, they and other lacteal constituents can be immunoregulatory. Immune protection of the MG largely depends on the innate immune system; the monocytes–macrophages group together with intraepithelial lymphocytes is dominant in the healthy gland. An increase in somatic cells (neutrophils) and various interleukins signal infection (mastitis) and a local immune response in the MG. The major role of the MG to mucosal immunity is the passive immunity supplied to the suckling neonate.

Evidence for a common mucosal immune system in the pig

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There is evidence that the common mucosal immune system exists in pigs.

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Vaccination at an easily accessible mucosal site may assist in providing protection at other mucosal sites.

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Local and distal mucosal sites should be sampled after vaccinations to define the optimal dose and formulation which promotes the common mucosal immune system in pigs.

The majority of lymphocytes activated at mucosal sites receive instructions to home back to the local mucosa, but a portion also seed distal mucosa sites. By seeding distal sites with antigen-specific effector or memory lymphocytes, the foundation is laid for the animal's mucosal immune system to respond with a secondary response should to this antigen be encountered at this site in the future. The common mucosal immune system has been studied quite extensively in rodent models but less so in large animal models such as the pig. Reasons for this paucity of reported induction of the common mucosal immune system in this species may be that distal mucosal sites were examined but no induction was observed and therefore it was not reported. However, we suspect that the majority of investigators simply did not sample distal mucosal sites and therefore there is little evidence of immune response induction in the literature. It is our hope that more pig immunologists and infectious disease experts who perform mucosal immunizations or inoculations on pigs will sample distal mucosal sites and report their findings, whether results are positive or negative. In this review, we highlight papers that show that immunization/inoculation using one route triggers mucosal immune system induction locally, systemically, and within at least one distal mucosal site. Only by understanding whether immunizations at one site triggers immunity throughout the common mucosal immune system can we rationally develop vaccines for the pig, and through these works we can gather evidence about the mucosal immune system that may be extrapolated to other livestock species or humans.

CCL28 involvement in mucosal tissues protection as a chemokine and as an antibacterial peptide

CCL28 chemokine is expressed by epithelial cells of various mucosal tissues. This chemokine binds to CCR3 and CCR10 receptors and plays an essential role in the IgA antibody secreting cells (IgA-ASC) homing to mucosal surfaces and to lactating mammary gland as well. In addition, CCL28 has been shown to exert a potent antimicrobial activity against both Gram-negative and Gram-positive bacteria and fungi. Using the pig model, we investigated the expression of both CCR10 and CCR3 receptors in a large panel of mucosal tissues. RT-PCR analysis revealed the expression of CCR3 and CCR10 mRNA in salivary glands, nasal mucosae, Peyer's patches, small and large intestine, suggesting the presence of leucocytes expressing these receptors within these tissues. CCR10 mRNA was observed in sow mammary gland at late gestation with an increasing level during lactation. Recombinant porcine CCL28 protein was produced and mass spectrometry analysis revealed antimicrobial chemokines features such as a high pI value (10.2) and a C-terminal highly positively-charged region. Using a viable count assay, we showed that CCL28 displayed antimicrobial activity against enteric pathogens and was effective in killing Salmonella serotypes Dublin and Choleraesuis, enteroinvasive Escherichia coli K88 and non-pathogenic E. Coli K12. The potent antimicrobial function of CCL28 combined with its wide distribution in mucosal tissues and secretions suggest that this protein plays an important role in innate immune protection of the epithelial surfaces.

Development of gut immunoglobulin A production in piglet in response to innate and environmental factors

The current review focuses on pre- and post-natal development of intestinal immunoglobulin A (IgA) production in pig. IgA production is influenced by intrinsic genetic factors in the foetus as well as extrinsic environmental factors during the post-natal period. At birth, piglets are exposed to new antigens through maternal colostrums/milk as well as exogenous microbiota. This exposure to new antigens is critical for the proper development of the gut mucosal immune system and is characterized mainly by the establishment of IgA response. A second critical period for neonatal intestinal immune system development occurs at weaning time when the gut environment is exposed to new dietary antigens. Neonate needs to establish oral tolerance and in the absence of protective milk need to fight potential new pathogens. To improve knowledge about the immune response in the neonates, it is important to identify intrinsic and extrinsic factors which influence the intestinal immune system development and to elucidate their mechanism of action.

Oral antigen exposure in extreme early life in lambs influences the magnitude of the immune response which can be generated in later life

BACKGROUND

Previous investigations in newborn lambs determined that adenovirus-mediated expression of antigen to a localized region of the gut induced antigen-specific mucosal and systemic immunity. These experiments were limited in that the localized region of the gut to which antigen was introduced was sterile and the influence of colostrum on the antigen was not assessed but they do suggest that mucosal vaccines may be an effective vaccination strategy to protect neonatal lambs. We propose that persistent oral antigen exposure introduced in extreme early life can induce immunity in lambs, despite the presence of commensal bacteria and colostrum.

RESULTS

To test this hypothesis, conventionally raised newborn lambs (n = 4 per group) were gavaged with ovalbumin (OVA) starting the day after birth for either a single day (2.27 g), every day for 3 days (0.23 g/day), or every day for 3 days then every second day until nine days of age (0.023 g/day). Lambs gavaged with OVA for 3 to 9 days developed significant serum anti-OVA IgG titres (p < 0.05), but not IgA titres, relative to control lambs (n = 4) after 3 and 4 weeks. At 4 weeks of age, lambs were immunized with OVA in Incomplete Freund's Adjuvant via intraperitoneal (i.p.) injection then lambs were euthanized at 7 weeks. Serum anti-OVA IgG titres were further augmented after i.p. immunization indicating immunity persisted and tolerance was not induced. Serum IgA titres remained low regardless of treatment. It is known that i.p. priming of sheep with antigen in Freund's complete adjuvant leads to an enhanced number of IgA and IgG antibody containing cells in the respiratory mucosa (Immunology 53(2):375-384, 1984). Lambs gavaged with a single bolus of 2.27 g OVA prior to i.p. immunization showed very low titres of anti-OVA IgA in the lung lavage. These data suggest that a single, high dose exposure to OVA can promote tolerance which impacts response to systemic vaccination in later life. Lambs gavaged with 0.023 g OVA for 9 days (Group C) generated significant anti-OVA IgA titres in lung (p < 0.001) compared to negative control lambs but no additive effect was observed compared to parenteral control lambs. When splenocytes were re-stimulated with OVA ex vivo, all groups failed to show increased lymphocyte proliferation or interferon (IFN)-γ production relative to the parenteral control group.

CONCLUSIONS

In agreement with our hypothesis, persistent low dose antigen exposure primes humoral antibody production in serum in conventionally raised newborn lambs. In contrast, a single high dose bolus of antigen triggered oral tolerance which negatively impacted the quality and magnitude of the immune response to i.p. immunization in later life. These tangential responses are important as they indicate that the dose and/or repeated oral exposure to antigen, such as that which may be found in the neonate's environment, may promote immunity or alternatively it may negatively impact responses to parenteral vaccination.

Induction of mucosal immunity by intranasal immunization with recombinant adenovirus expressing major epitopes of Porcine circovirus-2 capsid protein

Porcine circovirus-2 (PCV-2) is primarily transmitted through mucosa, thus the mucosal immunity may constitute an essential feature of vaccination strategies against PCV-2 infection. Mucosal immunity elicited by recombinant replication-deficient adenovirus expressing the major epitopes of PCV-2 capsid protein (rAd/Cap/518) via intranasal (i.n.), intramuscular (i.m.) or oral routes in mice were evaluated. Immunization with rAd/Cap/518 via i.n. route induced higher titers of IgA in saliva, bronchoalveolar and intestinal lavage fluid compared with those immunized via i.m. route. The proportions of CD3+, CD3+CD4+ and CD3+CD8+ T cells were significantly increased in mice immunized with rAd/Cap/518 via i.n. route compared with the control group. Higher levels of IFN-γ were detected in the spleen and mesenteric lymph nodes of mice immunized with rAd/Cap/518 via i.n. route compared with other groups, yet IL-4 was not detected in any group. Real-time PCR analysis confirmed viral DNA loads in the i.m. or i.n. immunization group was lower than that seen in the rAd immunization. These results indicate that i.n. administration of rAd/Cap/518 can elicit humoral and Th1-type cellular protective immunity in both systemic and mucosal immune compartments in mice, representing a promising mucosal vaccine candidate against PCV-2.

The mucosal immune system: recent developments and future directions in the pig

In most animals, the mucosal immune system effectively controls expression of active immune responses to pathogen and tolerance to harmless antigens. Our understanding of the function and control of the mucosal immune system has advanced as a result of studies in rodents and humans. The discoveries of regulatory T-cells and T-helper-17 cells, and studies on the interactions between epithelial and dendritic cells, demonstrate its complexity. In pigs, some of the systems and reagents for determining the relevance of these mechanisms are present, and indicate lines for future work. However, many empirical studies of the effect of manipulation of the mucosal immune system in the pig by prebiotics, probiotics and feed additives have been carried out. Interpretation of these results needs to be made with care, since manipulation of the mucosal immune system may improve its efficiency under a specific set of environmental and husbandry conditions, but impair it under others.

Identification in milk of a serum amyloid A peptide chemoattractant for B lymphoblasts

Background

Normal mammary gland contains an extravascular population of B lymphoblasts, precursors of the immunoglobulin plasma cells that play a key role in the passive protection of neonates by secreting immunoglobulins to colostrum and milk. We investigated the presence of chemoattractants in the milk by analysing the chemoattractant activity of various fractions of this secretion. Milk chemoattractants are potentially involved in the recruitment of lymphocytes from the maternal bloodstream in lactating mammary glands.

Results

The dilution-related lymphoid cell chemoattraction of whey was associated with a < 10 kDa ultrafiltrate. Active fractions were purified by reverse-phase high performance liquid chromatography. Two peptides of 2.7 kDa (DMREANYKNSDKYFHARGNYDAA) and 1 kDa (RPPGLPDKY) were identified as fragments of the SAA protein family, tentatively identified as SAA2. Only the 2.7 kDa synthetic peptide displayed chemotactic activity, at two different optimal concentrations. At the lower concentration (3.7 nM), it attracted B-cell lymphoblasts, whereas at the higher (3.7 μM), it attracted B lymphocytes. Then, the SAA mRNA expression was analysed and we observed more SAA transcripts during lactation than gestation.

Conclusion

These data are consistent with the SAA_23–45 fragment being involved in preplasma B-cell recruitment to the mammary gland and resultant benefit to the neonate.

Membrane markers of the immune cells in swine: an update

Besides their breeding value, swine are increasingly used as biomedical models. As reported in three international swine clusters of differentiation (CD) workshops and in the animal homologue section of the last workshop for the determination of human leukocyte differentiation antigens (HLDA 8), characterisation of leukocyte surface antigens by monoclonal antibodies and other molecular studies have determined the cell lineages and blood leukocyte subsets implicated in the immune response, including cell adhesion molecules involved in cell trafficking. This review focusses on the current state of knowledge of porcine leukocyte differentiation and major histocompatibility complex (SLA) molecules. Examples of porcine particularities such as the double-positive T lymphocytes with the phenotype CD(4+)CD8(low) and CD(4-)CD8(low) alphabeta T cell subsets and the persistence of SLA class II after T-lymphocyte activation are illustrated, as well as the shared characteristics of the Artiodactyla group, such as the high proportion of gammadelta TcR (T cell receptor) T cells in blood and other lymphoid tissues. Furthermore, discrepancies between swine and humans, such as CD16 expression on dendritic cells and CD11b (wCD11R1) tissue distribution are outlined. The rapidly growing information should facilitate manipulation of the swine immune system towards improving disease control, and open new avenues for biomedical research using the pig as a model.