Dietary l-Tryptophan Supplementation Enhances the Intestinal Mucosal Barrier Function in Weaned Piglets: Implication of Tryptophan-Metabolizing Microbiota.

l-Tryptophan (Trp) is known to play an important role in the health of the large intestine. However, a role of dietary Trp in the small-intestinal mucosal barrier and microbiota remains poorly understood. The present study was conducted with weaned piglets to address this issue. Postweaning piglets were fed for 4 weeks a corn- and soybean meal-based diet supplemented with 0 (Control), 0.1, 0.2, or 0.4% Trp. The small-intestinal microbiota and serum amino acids were analyzed by bacterial 16S rRNA gene-based high-throughput sequencing methods and high-performance liquid chromatography, respectively. The mRNA levels for genes involved in host defense and the abundances of tight-junction proteins in jejunum and duodenum were measured by real time-PCR and Western blot techniques, respectively. The concentrations of Trp in the serum of Trp-supplemented piglets increased in a dose-dependent manner. Compared with the control group, dietary supplementation with 0.2⁻0.4% Trp reduced the abundances of Clostridium sensu stricto and Streptococcus in the jejunum, increased the abundances of Lactobacillus and Clostridium XI (two species of bacteria that can metabolize Trp) in the jejunum, and augmented the concentrations of secretory immunoglobulin A (sIgA) as well as mRNA levels for porcine ß-defensins 2 and 3 in jejunal tissues. Moreover, dietary Trp supplementation activated the mammalian target of rapamycin signaling and increased the abundances of tight-junction proteins (zonula occludens (ZO)-1, ZO-3, and claudin-1) in jejunum and duodenum. We suggested that Trp-metabolizing bacteria in the small intestine of weaned pigs primarily mediated the beneficial effects of dietary Trp on its mucosal integrity, health, and function.

The origin of prostate gland-secreted IgA and IgG.

The prostate secretes immunoglobulin (Ig) A (IgA) and IgG; however, how immunoglobulins reach the secretion, where the plasma cells are located, whether immunoglobulins are antigen-specific and where activation of the adaptive response occurs are still unknown. Immune cells, including CD45RA+ cells, were scattered in the stroma and not organized mucosae-associated lymphoid-tissue. IgA (but not IgG) immunostaining identified stromal plasma cells and epithelial cells in non-immunized rats. Injected tetramethylrhodamine-IgA transcytosed the epithelium along with polymeric immunoglobulin receptor. Oral immunization with ovalbumin/mesopourous SBA-15 silica adjuvant resulted in more stromal CD45RA+/IgA+ cells, increased content of ovalbumin-specific IgA and IgG, and the appearance of intraepithelial CD45RA+/IgG+ cells. An increased number of dendritic cells that cooperate in other sites with transient immunocompetent lymphocytes, and the higher levels of interleukin-1ß, interferon-γ and transforming growth factor-ß, explain the levels of specific antibodies. Nasal immunization produced similar results except for the increase in dendritic cells. This immunomodulatory strategy seems useful to boost immunity against genitourinary infections and, perhaps, cancer.

Evaluation of the effects of a probiotic supplementation with respect to placebo on intestinal microflora and secretory IgA production, during antibiotic therapy, in children affected by recurrent airway infections and skin symptoms.

Antibiotic therapy, especially in pediatric patients, is often associated with significant modifications of the gut microflora, which can lead to intestinal dysbiosis and influence intestinal physiology and immune system functionality. Herein we report the results from a double blind controlled clinical trial in 77 pediatric patients affected by recurrent airway infections, receiving antibiotic therapy with amoxicillin and clavulanic acid. A group was treated with an oral probiotic preparation composed of Lactobacillus paracasei ssp.paracasei CRL-431, Bifidobacterium BB-12, Streptococcus thermophilus TH-4 and a fructooligosaccharide (FOS) during and after antibiotic therapy for seven days, while the other group received placebo. The study revealed a reduction in the Clostridia population, with a contemporary increase in Bifidobacteria and Lactobacilli in fecal samples in the probiotic group and an increase in the Enterobacteria population in the placebo group. Moreover, there was a decreasing trend in secretory IgA production in the probiotic group. Some relevant, but not statistically significant probiotic supplementation effects were identified.

Colostrum of healthy mothers contains broad spectrum of secretory IgA autoantibodies.

PURPOSE: Human colostrum and milk provide a newborn with immunomodulatory components, ensuring protection and proper development of the immune system. Secretory IgA antibodies in colostrum represent the first line of defence against harmful substances, but their potential spectra of reactivity with autoantigens remains unclear. Here, we characterised the repertoire of natural sectretory IgA autoantibodies in colostrum of healthy mothers. METHODS: The human colostrum samples from 39 healthy mothers were analyzed for autoantibodies by indirect immunofluorescence, dot blots, immunoblots and ELISA. RESULTS: We found that there is high diversity in reactivities of colostral IgA antibodies to autoantigens among individual samples. Using tissue sections and biochips commonly used for autoimmunity testing, we found that most samples reacted with monkey ovary (79.3%), monkey pancreatic tissue (78.6%), human HEp-2 cells (69%) and monkey adrenal gland (69.0%), fewer samples reacted with monkey liver tissue (47.2%), rat stomach (42.9%), monkey testicular tissue (41.4%), monkey salivary gland (39.3%), rat kidney (32.1%) and monkey cerebellar tissue (17.9%). At the protein level, we detected reactivity of IgA with 21 out of 25 (auto) antigens. The majority of the samples reacted with the pyruvate dehydrogenase complex, E3 ubiquitin ligase, cytosolic liver antigen, promyelocytic leukemia protein and nuclear pore glycoprotein-210. Using ELISA, we found reactivity of colostral IgA antibodies against examined extractable nuclear antigens, double stranded DNA, phospholipids and neutrophil cytoplasm. CONCLUSIONS: The broad spectrum of polyreactive natural autoantibodies present in human colostrum may contribute to proper development of mucosal immune system of the breastfed infant.

Vaccination strategies to promote mucosal antibody responses.

There are great interest and demand for the development of vaccines to prevent and treat diverse microbial infections. Mucosal vaccines elicit immune protection by stimulating the production of antibodies at mucosal surfaces and systemic districts. Being positioned in close proximity to a large community of commensal microbes, the mucosal immune system deploys a heterogeneous population of cells and a complex regulatory network to maintain the balance between surveillance and tolerance. A successful mucosal vaccine relies on leveraging the functions of these immune cells and regulatory components. We review the important cellular interactions and molecular pathways underlying the induction and regulation of mucosal antibody responses and discuss their implications on mucosal vaccination.

Intranasal immunization with phosphorylcholine induces antigen specific mucosal and systemic immune responses in mice.

Phosphorylcholine (PC) is a structural component of a wide variety of pathogens including Streptococcus pneumoniae and Haemophilus influenzae, and anti-PC immune responses are known to protect mice against invasive bacterial diseases. The present study tested the capability of PC as an intranasal plurispecific vaccine against upper airway infections. BALB/c mice immunized with intranasal PC-keyhole limpet hemocyanin (KLH) plus cholera toxin (CT) as a mucosal adjuvant showed increased PC-specific IgM in serum, IgA in nasal wash and saliva, and numbers of PC-specific nasal and splenic antibody producing cells. Enhanced production of IL-4 and IFN-gamma by CD4+ T cells indicated the participation of Th2- and Th1-type cells. Salivary IgA antibodies produced by intranasal immunization with PC-KLH plus CT reacted to most strains of S. pneumoniae and H. influenzae. Further we demonstrated that the clearance of S. pneumoniae and H. influenzae from the nasal tract was significantly enhanced by nasal immunization with PC-KLH and CT. Thus, intranasal vaccination to induce PC-specific immune responses might help to prevent upper airway infections caused by S. pneumoniae and H. influenzae.

Production of salivary immunoglobulin A and suppression of Dermatophagoides pteronyssinus-induced airway inflammation by local nasal immunotherapy.

BACKGROUND: Local nasal immunotherapy (LNIT) is an effective immunotherapeutic modality, especially when targeting a single immunodominant peptide from an allergen. However, the working mechanisms of LNIT are poorly understood. We hypothesized that LNIT with a mixture of group 2 allergens of Dermatophagoides pteronyssinus (Der p 2) protein and fungal immunomodulatory peptide (FIP) would generate suppression of Der p-induced airway inflammation through immunoglobulin (Ig) A secretion in the airways. METHOD: Mice were sensitized with recombinant Der p 2 (rDer p 2) and Der p followed by LNIT with rDer p 2 in conjunction with FIP. After intratracheal challenge with rDer p 2 and Der p, the airway inflammation was determined by analyzing the cell subpopulation and cytokine concentration in the bronchoalveolar lavage fluid. The allergen-specific IgE, IgG2a and IgG in the sera and IgA in the saliva were measured by ELISA. RESULTS: LNIT with rDer p 2 in conjunction with FIP could downregulate the lymphocyte infiltration in both rDer p 2- and Der p-induced airway inflammation. Both total and specific IgA in the saliva were increased after LNIT. Serum levels of IL-4, IL-10 and specific IgE were reduced and the specific IgG2a and IgG increased after LNIT. After LNIT, there was a reduction of airway hypersensitivity at 30 min after allergen challenge in the rDer p 2-and Der p-sensitized mice, with a significant decrease only in rDer p 2-sensitized mice. CONCLUSION: LNIT with rDer p 2 in conjunction with FIP was not only able to suppress rDer p 2-induced airway inflammation but also generate suppression of Der p-induced airway inflammation. The simultaneous reduction of IL-4 and IL-10 indicated that IL-10-producing cells were not activated by LNIT. The increment of IgA in the airway might play a role in the prevention of airway inflammation.

The effects of music listening after a stressful task on immune functions, neuroendocrine responses, and emotional states in college students.

The purpose of this study was to examine the effects of listening to high-uplifting or low-uplifting music after a stressful task on (a) immune functions, (b) neuroendocrine responses, and (c) emotional states in college students. Musical selections that were evaluated as high-uplifting or low-uplifting by Japanese college students were used as musical stimuli. Eighteen Japanese subjects performed stressful tasks before they experienced each of these experimental conditions: (a) high-uplifting music, (b) low-uplifting music, and (c) silence. Subjects' emotional states, the Secretory IgA (S-IgA) level, active natural killer (NK) cell level, the numbers of T lymphocyte CD4+, CD8+, CD16+, dopamine, norepinephrine, and epinephrine levels were measured before and after each experimental condition. Results indicated low-uplifting music had a trend of increasing a sense of well-being. High-uplifting music showed trends of increasing the norepinephrine level, liveliness, and decreasing depression. Active NK cells were decreased after 20 min of silence. Results of the study were inconclusive, but high-uplifting and low-uplifting music had different effects on immune, neuroendocrine, and psychological responses. Classification of music is important to research that examines the effects of music on these responses. Recommendations for future research are discussed.

Concentrated bovine colostrum protein supplementation reduces the incidence of self-reported symptoms of upper respiratory tract infection in adult males.

BACKGROUND: Anecdotal reports suggest that bovine colostrum may prevent upper respiratory tract infection (URTI). There is scant evidence to support such claims, although salivary IgA protects against URTI, and it was recently shown that bovine colostrum increases salivary IgA. AIM OF THE STUDY: The present invesigation examined whether concentrated bovine colostrum protein (CBC) affected the incidence or duration of self-reported symptoms of URTI in adult males. METHODS: We examined logbooks containing self-reported symptoms of illness from previous studies which examined physiological effects of CBC. In these double-blind, placebo controlled studies, subjects had been randomly allocated to consume 60g. day(-1) of CBC (n = 93) or whey protein (WP) (n = 81) for eight weeks. Symptoms were coded using established criteria to identify those related to URTI. Since the incubation period for an URTI is up to five days, symptoms reported during the first week of supplementation (PRE-EXP) were analysed separately to preclude those arising from infection prior to study commencement. RESULTS: During PRE-EXP, there was no difference in the proportion of subjects taking the different supplements who reported symptoms of URTI (CBC, 11%,WP, 5%; 95% Confidence Interval (95% CI) -14% to 2%; P = 0.16). During the subsequent seven weeks (i. e. the experimental period), a significantly lesser proportion of subjects taking CBC reported symptoms of URTI compared with those taking WP (CBC, 32%,WP, 48%, P = 0.03; 95 % CI -30 % to -2 %), but symptom duration did not differ (CBC, 6.8 +/- 4.2 days,WP, 6.0 +/- 4.4 days; P = 0.27). CONCLUSION: This study provides preliminary evidence that CBC may enhance resistance to the development of symptoms of URTI.

Dietary supplementation with vitamin E modulates avian intestinal immunity.

The effect of dietary vitamin E on immunoglobulin A (IgA) antibody production, which acts as the first line of defence at the intestinal mucosa, has not been evaluated in chickens. In the present study the impact of the inclusion of supplementary levels of vitamin E to the diet, on total and antigen-specific IgA antibody titres, T-cell subsets and Ia+ cells, was assessed. From hatching, chickens received a maize-based diet which was supplemented with either 25, 250, 2500 or 5000 mg dl-alpha-tocopherol acetate/kg. Primary immunisation with tetanus toxoid (T. toxoid) emulsified in a vegetable oil-in-water adjuvant was administered by the intraperitoneal route at 21 d of age. At 35 d of age all birds received an oral booster vaccination of T. toxoid. Significantly higher total IgA antibody titres were present in the day 42 intestinal scrapings of birds receiving the 5000 mg/kg vitamin E-supplemented diet (VESD) (P=0.05) and a notable increase was observed in birds receiving the 250 mg/kg VESD (P=0.06). At days 21 and 42 total serum IgA antibody titres of birds receiving the 250 mg/kg VESD was significantly higher (P<0.05) than the control birds. Following immunisation with T. toxoid, birds receiving the 250 and the 5000 mg/kg VESD had elevated anti-T. toxoid IgA antibody titres in final day intestinal scrapings, which, for the latter group was statistically significant (P=0.02). Both of these groups also demonstrated increased titres of anti-T. toxoid IgA in the serum at day 42. Birds receiving the 250 mg/kg VESD exhibited a notable increase in the percentage of T-helper cells and Ia+ cells in peripheral blood on day 26. The results illustrate the potential for some levels of dietary vitamin E supplementation to act as an immunomodulator of total and antigen-specific IgA antibody.

Impaired vitamin A-mediated mucosal IgA response in IL-5 receptor-knockout mice.

To clarify actions of vitamin A on mucosal immunity associated with interleukin-5 (IL-5), we examined effects of vitamin A on mucosal IgA level in IL-5 receptor alpha-chain-knockout (IL-5Ralpha(-/-)) mice. Daily supplementation of retinyl acetate (1 mg/mouse) increased Th2 cytokine levels and a number of their positive cells in the small intestinal mucosa of IL-5Ralpha(-/-) mice, as observed in wild-type or IL-5Ralpha(+/-) mice. Wild-type and heterozygous mice increased the IgA level and a number of IgA-containing cells in the mucosa in response to the vitamin A treatment, but not in IL-5Ralpha(-/-) mice. Retinyl acetate increased anti-cholera toxin (CT) IgA level in the mucosa of wild-type mice, improving their survival rate after an exposure to 0.4 mg of CT. However, retinyl acetate failed to induce resistance to CT toxicity in IL-5Ralpha(-/-) mice. Our results suggest that IL-5 may play an important role in an action of vitamin A on mucosal IgA system.

The identification of plant lectins with mucosal adjuvant activity.

To date, the most potent mucosal vaccine adjuvants to be identified have been bacterial toxins. The present data demonstrate that the type 2 ribosome-inactivating protein (type 2 RIP), mistletoe lectin I (ML-I) is a strong mucosal adjuvant of plant origin. A number of plant lectins were investigated as intranasal (i.n.) coadjuvants for a bystander protein, ovalbumin (OVA). As a positive control, a potent mucosal adjuvant, cholera toxin (CT), was used. Co-administration of ML-I or CT with OVA stimulated high titres of OVA-specific serum immunoglobulin G (IgG) in addition to OVA-specific IgA in mucosal secretions. CT and ML-I were also strongly immunogenic, inducing high titres of specific serum IgG and specific IgA at mucosal sites. None of the other plant lectins investigated significantly boosted the response to co-administered OVA. Immunization with phytohaemagglutinin (PHA) plus OVA elicited a lectin-specific response but did not stimulate an enhanced response to OVA compared with the antigen alone. Intranasal delivery of tomato lectin (LEA) elicited a strong lectin-specific systemic and mucosal antibody response but only weakly potentiated the response to co-delivered OVA. In contrast, administration of wheatgerm agglutinin (WGA) or Ulex europaeus lectin 1 (UEA-I) with OVA stimulated a serum IgG response to OVA while the lectin-specific responses (particularly for WGA) were relatively low. Thus, there was not a direct correlation between immunogenicity and adjuvanticity although the strongest adjuvants (CT, ML-I) were also highly immunogenic.

The induction of systemic and mucosal immune responses following the subcutaneous immunization of mature adult mice: characterization of the antibodies in mucosal secretions of animals immunized with antigen formulations containing a vitamin D3 adjuvant.

Systemic and mucosal immune responses were effectively induced following the subcutaneous administration of Haemophilus influenzae type b oligosaccharide conjugated to diphtheria toxoid vaccine in a formulation containing the active form of vitamin D3. IgA and IgG antibodies with specificity for both the protein and oligosaccharide components of the vaccine were detectable in mucosal secretions following immunization. The IgA and IgG mucosal antibodies were produced locally, and were functional as demonstrated by their diphtheria toxin neutralizing activity. Our data suggests that subcutaneous tissues can effectively serve as effective antigen presenting sites for both mucosal and systemic immune responses to antigens administered in combination with vitamin D3.

Oral immunotherapy with short ragweed extract in a novel encapsulated preparation: a double-blind study.

BACKGROUND: In the past, oral immunotherapy with allergens has had limited clinical effectiveness, presumably because of gastrointestinal destruction of allergens. OBJECTIVE: We have developed a new technique for microencapsulating protein antigens that permits them, when given orally, to bypass the stomach and be delivered to the small intestine in a highly immunogenic form. This study's purpose was to confirm the immunologic potency of orally administered short ragweed pollen extracts (SRW) microencapsulated (mSRW) by this new technique and to study the effectiveness of mSRW in controlling the symptoms of ragweed-induced hay fever. METHODS: Twenty-one SRW-sensitive patients were treated with mSRW in a double-blind placebo-controlled study. Serum SRW IgG and IgE antibodies and nasal secretory IgA antibodies were determined. During the ragweed season, symptoms were quantified by symptom-medication scoring. RESULTS: The treated patients had high titers of serum SRW IgG antibodies (1.15 microg/ml at baseline, increasing to 21.21 microg/ml), experienced regulation of the seasonal increase in serum SRW IgE antibodies (+9% vs +59% in placebo-treated patients), and produced a small amount of nasal SRW IgA antibodies. Despite an insubstantial pollen count, the symptom-medication scores in the treated group were lower than those in the placebo group (4.28 vs 6.18, p = 0.059), but the differences were statistically significant only in the subgroup that tolerated high doses (>20 microg of Amb a 1 in 19 of 21 patients, p = 0.04). These effects were accomplished without inducing any systemic reactions with a dose of mSRW (mean, 23.8 microg of Amb a 1) only slightly higher than that used in high-dose subcutaneous immunotherapy. CONCLUSION: Oral mSRW seems a safe, easily administered, and immunologically potent treatment for ragweed-induced hay fever, but its ultimate utility requires further study.

Induction of oral tolerance after feeding of ragweed pollen extract in mice.

The induction of oral tolerance following the feeding of ragweed pollen and its extract was investigated in BALB/c mice. Antibody class-specific immune suppression could be observed, and the IgE response was specifically suppressed, depending on the amount of ragweed pollen extract fed when subsequently immunized with ragweed extract together with A1(OH)3 as an adjuvant. A multiple feeding was more effective than a single feeding of antigen, and the IgE response was completely suppressed when 20 mg of pollen extract was fed for 5 consecutive days. On the other hand, IgG production was not suppressed even though a large amount of ragweed pollen or its extract was fed. Furthermore, no secretion of antigen-specific IgA into saliva was observed in control animals or those fed ragweed pollen extract. Thus, pollen extract feeding may be potentially useful for the prophylaxis or therapy of allergic rhinitis induced by ragweed.

Glutamine in parenteral solutions enhances intestinal mucosal immune function in rats.

Biliary secretory immunoglobulin A (sIgA) and proportions of IgA+ plasma cells, helper T cells, and suppressor/cytotoxic T cells in intestinal tissue were lower in rats receiving a standard total parenteral nutrition (TPN) solution than in those receiving TPN enriched with glutamine. Parenteral solutions supplemented with glutamine may preserve the ability of intestinal immune tissue to produce sIgA-synthesizing plasma cells following antigenic stimulation.

Transformation of human colostrum lymphocytes with Epstein-Barr virus.

Lymphocytes from human colostrum were transformed with EB virus to obtain immunoglobulin secreting cells. Equal proportions of IgG, IgA and IgM were detected in wells containing transformed colostrum cells. Pretreatment of colostrum cells with BCGF prior to EB virus infection reduced the transformation slightly. We discussed the possibility of establishing cell lines that produced human monoclonal antibody using colostrum cells.

Use of Peyer's patch and lymph node fragment cultures to compare local immune responses to Morganella morganii.

Lymphoid tissue fragment cultures were established to analyze the differentiative processes among B cells in Peyer's patches (PP) and peripheral lymph nodes (PLN), especially those in germinal centers. PP cultures from both conventionally reared mice and formerly germ-free mice colonized with Morganella morganii could be maintained for greater than 12 days with continued B-cell division, especially among cells binding high levels of peanut agglutinin, a characteristic of germinal center cells. PLN cultures from conventionally reared mice injected with a heat-killed vaccine of M. morganii could be maintained for the same amount of time. Over this period, PP cultures continued to secrete immunoglobulin A (IgA) as well as smaller amounts of IgM. PP cultures from formerly germ-free mice colonized with M. morganii showed net increases of IgA antiphosphocholine (anti-PC) antibodies with avidities as high as those of the prototypic T15 monoclonal antibody. Similar PLN fragment cultures from conventionally reared mice given footpad injections of M. morganii showed net increases of IgM and IgG anti-PC antibodies in the culture fluid. Thus, although M. morganii stimulated lymphoid tissues in vivo to produce an anti-PC response in vitro when given by either the oral or the parenteral route, the antibody isotypes differed between PP and PLN fragment cultures. Fragment culturing may offer a complementary and simpler way to detect a local secretory IgA response than does either measuring IgA antibody in secretions or detecting IgA antibody in the cytoplasm of plasma cells in the lamina propria of gastrointestinal or respiratory tissue.

Effect of immune system imagery on secretory IgA.

This study was an investigation of the effects of physiologically-oriented mental imagery on immune functioning. College students with normal medical histories were randomly selected to one of three groups. Subjects in Group 1 participated in short educational training on the production of secretory immunoglobulin A. They were then tested on salivary IgA, skin temperature, and the Profile of Mood States (POMS) before and after listening to a 17-minute tape of imagery instructions with specially composed background "entrainment" music designed to enhance imagery. Subjects in Group 2 (placebo controls) listened to the same music but received nor formal training on the immune system. Group 3 acted as a control and subjects were tested before and after 17 minutes of no activity. Treatment groups listened to their tapes at home on a bi-daily basis for six weeks. All groups were again tested at Weeks 3 and 6. Secretory IgA was analyzed using standard radial immunodiffusion techniques. Repeated measures analyses of variance with planned orthogonal contrasts were used to evaluate the data. Significant overall increases (p less than 0.05) were found between pre- and posttests for all three trials. Groups 1 and 2 combined (treatment groups) yielded significantly greater increases in sIgA over Group 3 (control) for all three trials. Group 1 (imagery) was significantly higher than Group 2 (music) in antibody production for Trials 2 and 3. Symptomatology, recorded by subjects at Weeks 3 and 6, was significantly lower for three symptoms (rapid heartbeat, breathing difficulty, and jaw clenching), favoring both treatment groups over the control group.

K88 variants K88ab, K88ac and K88ad in oral vaccination of different porcine adhesive phenotypes. Immunological aspects.

Sows of different adhesive phenotypes were vaccinated orally during the last 4 weeks of gestation with K88-positive Escherichia coli. Sows susceptible to adhesion by the K88 variant of the vaccination strain produced a significant IgA-class specific anti-K88 response in colostrum and milk and post-farrowing serum. Indications for an IgM and IgG-class specific anti-K88 response were also found in this group but only in milk. In sows resistant to adhesion by the K88 variant of the vaccination strain only an IgA-class specific anti-K88 antibody response was found in mammary secretions and in post-farrowing sera, but titres did not reach the high values of the former group. The response in the second group was attributed to the frequent administration of large quantities of K88-positive E. coli which to some extent can be compared with a colonization effect. Specificity for the serological components of the K88 variants was detectable in colostral IgA of sows susceptible to the vaccination strain only.