The pig histocompatibility system SLA: serological study on a group of antigenic specificities

Swine leukocyte antigen (SLA) diversity in Sinclair and Hanford swine

The swine leukocyte antigen (SLA) haplotype B is associated with increased penetrance of the tumor traits in Sinclair swine cutaneous melanoma (SSCM). We established a series of SinclairxHanford swine crosses to facilitate genetic mapping of the tumor-associated loci. In this study, the SLA diversity in the founding animals was characterized for effective selection of maximum tumor penetrance in the pedigrees. Using the sequence-based typing (SBT) method we identified a total of 29 alleles at five polymorphic SLA loci (SLA-1, SLA-3, SLA-2, DRB1 and DQB1) representing six class I and five class II haplotypes. We subsequently developed a rapid PCR-based typing assay using sequence-specific primers (PCR-SSP) to efficiently follow the SLA types of the crossbred progeny. In a total of 469 animals we identified three crossovers within the class I region and three between the class I and class II regions, which corresponded to recombination frequencies of 0.39% and 0.56%, respectively. We also confirmed the presence of two expressed SLA-1 loci in three of the class I haplotypes and were able to determine the relative chromosomal arrangement of the duplicated loci in two haplotypes. This study furthers our understanding of the allelic architecture and polymorphism of the SLA system and will facilitate the mapping of loci associated with the expression of SSCM.

Detection of a new non-MHC alloantigenic system (SLD) in pigs

A new, non-MHC cell membrane leucocyte alloantigen was detected in pigs by the complement dependent lymphocytotoxic technique. The new leucocyte system was designated SLD. Its product antigen SLD-1 was demonstrated to segregate independently of the SLA, SLB, SLC, A and E antigens. Family studies supplied evidence of a dominant inheritance of SLD-1. Since an allelic antigen could not be demonstrated, only two alleles for this locus are reported, namely SLD1 and SLD-. No evidence of linkage was detected between the above mentioned leucocyte alloantigenic systems and SLD. The antigen was detected on enriched suspensions of T and B cells from peripheral blood, but it was not detected on erythrocytes, granulocytes and thrombocytes.

The swine histocompatibility system SLA: serological studies in the common Swiss and Danish swine breeds

Alloantisera were produced in common Swiss and Danish swine breeds by immunization with leucocytes or skin-grafts. Out of the 126 antisera, 66 were chosen for further study based on titrations employing lymphocytes from unrelated pigs typed with French SLA antisera (Vaiman, Chardon & Renard, 1979). The 66 selected antisera and the French reagents defining 26 SLA specificities were used to type lymphocytes from 595 unrelated pigs of the common Swiss and Danish breeds. The reaction-patterns of the French, Swiss and Danish antisera were adequately correlated for the French SLA specificities Nos FJ 2, 3, 6, 7, 8, 9, 11, 14, 19, 20 and 24 and for the haplotypes FJ 15.1.18 and FJ 5.4. In addition, a cluster of correlated Danish and Swiss antisera characterized a new specificity, provisionally designated CPH 31. This specificity was frequent in the Danish Landrace pigs. Using the reagents identified in this report, the segregation of SLA markers was studied. Back-cross families demonstrated segregation of 15 distinct SLA haplotypes of which 14 are common in French Landrace or Large White. Differences were found in haplotype frequencies in both the Swiss and the Danish Landrace and Large White breeds.

Polymorphism of the SLB serologically defined (non-MHC) alloantigenic system in pigs

Six new antigenic specificities (designated SLB-2 to SLB-7) detectable with polyclonal reagents in the complement-dependent lymphocytotoxic test were determined in the SLB alloantigenic system of pigs. The SLB specificities (including the previously described SLB-1) are controlled by 13 alleles. An analysis of a further 121 double backcross matings (with 817 offspring) confirmed that the products of SLB alleles segregated independently of the SLA haplotypes (swine MHC). In addition, in 112 families of the same mating type (with 746 progeny) the map distance of the SLB locus and the highly polymorphic L blood group locus was found to be 7.82 centimorgans in the heterogametic sex and 12.57 centimorgans in the homogametic sex.

Preliminary evidence of segregation distortion in the SLA system

The segregation of 11 well-defined SLA haplotypes was investigated in 40 Land-race and 48 Large White Danish and Swiss litters. Among the 11 haplotypes, the segregation of one (SLA 20-8.2.11) deviated significantly from the expected 1:1 segregation ratio in back-cross families. Tests indicated that these families were homogeneous with respect to segregation distortion, although the distortion was more pronounced in litters sired by heterozygous Danish boars than by heterozygous Swiss boars and Danish and Swiss sows. The data presented do not allow any definite conclusion about the cause of the segregation distortion. The possibility of the distortion being caused either by a complex similar to the T/t-complex found in mouse and contemplated in man or directly by the SLA region is discussed.

Molecular characterization of swine leucocyte antigen class I genes in outbred pig populations

The highly polymorphic swine leucocyte antigen (SLA) genes are one of the most important determinants in swine immune responses to infectious diseases, vaccines, and in transplantation success. Study of SLA influence requires accurate and effective typing methods. We developed a simple and rapid method to type alleles at the three classical SLA class I loci (SLA-1, SLA-3 and SLA-2) using the PCR-sequence-specific primer (PCR-SSP) strategy. This typing system relies on 47 discriminatory PCR primer pairs designed to amplify the SLA class I alleles by groups that have similar sequence motifs. We applied this low-resolution group-specific typing method to characterize the SLA class I alleles present in three outbred pig populations (n = 202). Alleles from 24 class I allele groups corresponding to 56 class I genotypes were detected. We also identified 23 low-resolution SLA class I haplotypes in these pigs and found haplotypes Lr-1.0 (SLA-1*01XX-SLA-3*01XX-SLA-2*01XX) and Lr-4.0 (SLA-1*04XX-SLA-3*04XX-SLA-2*04XX) in all three pig populations with a high prevalence. Over 80% of the pigs examined (n = 162) were found to bear at least one of these haplotypes, resulting in a combined haplotype frequency of nearly 50%. This PCR-SSP-based typing system demonstrates a reliable and unambiguous detection of SLA class I alleles, and can be used to effectively investigate the SLA diversity in outbred pig populations. It will help to identify the role of SLA antigens in disease-resistant pigs and may facilitate the development of effective vaccines.

Characterization of a new porcine differentiation antigen involved in the proliferative response to mitogens

The cytotoxic monoclonal antibody (Mab) LIL 13 reacts with a widely distributed antigen that is expressed on 80-95% of swine peripheral blood mononuclear cells (PBMC) and a variety of lymphoid cell types. Using indirect immunofluorescence (IIF) the positive cells (75-100%) were divided between the bright, intermediate and dull populations. The remaining negative cell population contained B-cells, T-cells and probably null cells. Mab LIL 13 did not react with swine major histocompatibility complex (MHC) class I antigens (SLA) and did not inhibit E-rosette formation. Reactivity of LIL 13 with leukocyte function antigen 1 (LFA-1) was excluded by competitive IIF and cytotoxicity tests with cross-reacting anti-human CD 18 or anti-swine LFA-1-specific antibodies. Mab LIL 13 and complement treatment severely reduced mitogen-induced proliferative response to phytohaemagglutinin (PHA), concanavalin A (Con A), pokeweed mitogen (PWM) and lipopolysaccharide (LPS) (90-100%). In the absence of complement, LIL 13 partially reduced proliferation of cells by interfering with the capability of mitogens to bind to the corresponding surface receptor (LIL 13 followed by mitogens), and partially inhibited mitogenic proliferative response following post-treatment (mitogens followed by LIL 13). Biochemical analysis of the antigen using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed bands of approximately 180-190 kDa and 46-50 kDa under reducing conditions and 200 kDa and 46-50 kDa under nonreducing conditions.

Swine lymphocyte alloantigens (SLA) class I serology and genetics in Belgian Landrace and Pietrain breeds

Eighty anti-SLA class I reagents were prepared resulting from skin graft and subcutaneous immunizations in 320 fattening pigs of the Belgian Landrace and Pietrain breeds. By means of these alloantisera seven internationally and five locally established specificities were recognized. Three of the locally assigned specificities were new: BM 36, BM 37 and BM 38. They were serologically and genetically defined. The typing battery was completed with French and Danish reagents, and correlation coefficients were calculated for the main alloantisera recognizing SLA class I alloantigens observed in the Belgian breeds. The SLA haplotype frequencies were estimated in 372 Belgian Landrace and 369 Pietrain pigs. The SLA haplotype distribution differs significantly between both breeds and the genetic distance (0.54) at the SLA system is quite high.

Molecular genetic analyses of the major histocompatibility complex in pig families and recombinants

Five HLA probes, one corresponding to class I genes, two corresponding to distinct class II light chain genes, DR beta and DQ beta, and two to class II heavy chain genes, DR alpha and DQ alpha, were used to analyse the genomic DNA of the pig. Three informative SLA typed families and four SLA recombinants were studied by Southern blot analysis. About 16 restriction fragments, generated by EcoR1 or Hind III endonucleases, were revealed for each individual, either with the class I probe or the DR beta probe. The number of restriction fragments which hybridized with the other probes was generally lower. Several restriction fragment-length polymorphisms were found and these segregated with SLA haplotypes. The studies on SLA recombinants showed that SLA DR beta- and DQ alpha-like genes are probably tightly clustered within the SLA-D-MLR region.

Restriction fragment length polymorphism of the major histocompatibility complex of the pig

Human HLA cDNA probes were used to analyze the restriction fragment length polymorphism (RFLP) of the SLA major histocompatibility complex in swine. Cellular genomic DNA from 19 SLA homozygous pigs representing 13 different haplotypes was digested with restriction endonucleases Eco R1, Hind III, or Bam H1, separated by electrophoresis, and transferred onto diazobenzyloxymethyl paper by the Southern blot technique. The blots were probed with 32P-labeled class I or beta-DR class II cDNA. Depending on the haplotypes and the endonucleases used, seven to ten restriction fragments hybridized with the class I probe, and five to seven with the beta-DR probe. Their sizes ranged from 3.4 to 22 kilobase-pairs. Few bands were common to all 13 haplotypes. With all but one haplotype, identical autoradiogram patterns were obtained from unrelated, but phenotypically SLA-identical pigs, suggesting that most of the RFLP revealed were controlled by the SLA region. Further polymorphism was found in a group of seven unrelated pigs which typed serologically as SLA A15 C1 B18 homozygotes but could be divided into two subgroups, with five animals in one subgroup and two in the other, when the genomic DNA was hybridized with the class I probe. When the class II beta-DR probe was tested on the same seven pigs, another subdivision was seen, and this correlated with MLR data. These results demonstrate that HLA class I and class II probes can be used to identify certain well-established SLA haplotypes and to identify subclasses within at least one SLA haplotype.