Cross-reactivity between RSV-induced tumor antigen and B5 MHC alloantigen in the chicken

Lymphocytes from chickens homozygous (B ² B ²) at the major histocompatibility complex (MHC) were tested for cytotoxic activity against five types of target chicken embryo fibroblasts (CEF). Lymphocytes from B²B² chickens bearing RSV-induced tumors lysed in vitro targets of B ² B ² and B ⁵ B ⁵ RSV-infected CEF and B ⁵ B ⁵ normal CEF, but did not lyse B ² B ² and B ²⁴ B ²⁴ normal CEF. Lymphocytes from normal B ² B ² chickens did not lyse any of the five types of CEF targets. Alloantisera absorption studies showed that both RSV-infected and uninfected CEF shared alloantigens, in particular B-F alloantigens, with syngeneic erythrocytes. Absorption with B ² B ² RSV-infected CEF significantly lowered the titer of B ² B ² anti-B ⁵ B ⁵ alloantisera. Cross-reactivity between B ₅ antigen(s) and tumor-associated antigen was suggested and the nature of the cross-reactivity was discussed. It is hypothesized that this cross-reactivity prevents B ⁵ B ⁵ chickens from recognizing RSV-induced tumors as foreign, enhances tumor growth and leads to death of the host.     

Influence of different B-complex recombinants on the outcome of Rous sarcomas in chickens

Seven major histocompatibility (B) complex recombinants were evaluated for anti-Rous sarcoma response. In experiment 1, the B^R5(F21-G19) recombinant haplotype both homozygous and in heterozygous combinations with B¹⁹ and B²¹ haplotypes were compared to B¹⁹/B¹⁹ and B²¹/B²¹ chickens to determine the relative influence of the B^F versus B^G chromosomal segments on regression of Rous sarcoma virus-induced tumours. In experiment 2, six recombinant haplotypes B^R1(F24-G23), B^R2(F2-G23), B^R3(F2-G23), B^R4(F2-G23), B^R6(F21-G23) and B^R8(F2-G2a,23) present in chickens heterozygous for normal haplotypes B¹⁹, B²³ or B²⁶ were compared for anti-sarcoma response. A total of 1328 chickens were blood typed for B alloanti-gens at 17 days of age, inoculated in the wingweb with Rous sarcoma virus at 6 weeks and monitored for anti-tumour immune response over a 10-week period. Genotypes which shared the same B^F haplotype, but differed in their B^G regions, had similar anti-tumour responses, implicating the B^F but not the B^G region in tumour regression. Chickens carrying B^F2 or B^F21 had a strong anti-tumour response, while B^F24 conferred a weaker response, regardless of the accompanying normal haplotype.     

Mapping of susceptibility to Marek's disease within the major histocompatibility (B) complex by refined typing of White Leghorn chickens

The major histocompatibility (B) complex of a distinct commercial pure White Leghorn chicken line was characterized using serological, biochemical and restriction fragment length polymorphism (RFLP) typing. Line B chickens displayed a high recombination frequency within the B complex. Three recombinant haplo-types were identified. The influence of these haplotypes was determined in relation to the haplotypes B^l9 and B²¹ on their resistance to Marek's disease (MD) in an experimental infection with the virus. Offspring of sires with a recombinant haplotype in combination with B¹⁹ or B²¹, and dams, which were homozygous B¹⁹/B¹⁹ or B²¹/B²¹ were infected. The B type of the offspring had a significant effect upon survival. Animals with B complex types B²¹/B²¹, B¹³⁴/B²¹ and B²³⁴/B²¹ were relatively resistant to MD (24–32% mortality), whereas B¹⁹/B¹⁹ birds were highly susceptible (68% mortality). Animals with a recombinant halpotype B^19r21 (B-G²¹, B-F¹⁹) were equally susceptible to MD as birds with the complete B¹⁹ haplotype. In contrast to earlier publications, resistance was not inherited as a dominant trait. Apparently, B¹⁹ was associated with a dominant susceptibility. The gene(s) associated with the B complex and involved in resistance to MD were localized within the B-F/B-L region. However, the association with a presumably non-coding subregion of B-G could not be excluded.     

Major histocompatibility (B) complex effects on acquired immunity to cecal coccidiosis

The influence of the major histocompatibility (B) complex on acquired immunity to the avian coccidium Eimeria tenella was studied in 217 F₄ segregants (B ² B ², B ² B ⁵, B ⁵ B ⁵) of a cross between inbred lines 6₁ (B ² B ²) and 15₁ (B ⁵ B ⁵) and segregating haplotype combinations of UNH105 (B ²³ B ²³ B ²³ B ²⁴, B ²⁴ B ²⁴), a noninbred line of New Hampshire chickens. Chickens were immunized at 6 weeks of age with 500 oocysts daily for 5 days, then challenged 14 days later with 10000 oocysts. Responses to infection were evaluated by cecal lesion scores, body weight gain, delayed wattle reaction (DWR), and spleen weight. The F₄ segregants of genotypes B ² B ⁵ and B ⁵ B ⁵ exhibited greater immunity to challenge than B ² B ² chickens. B ⁵ B ⁵ chickens showed a significantly greater DWR following immunization and larger spleens 6 days after the challenge than either of the other genotypes. However, both BIBS and B ⁵ B ⁵ chickens demonstrated significantly lower lesion scores than B ² B ² chickens. There were no significant differences in weight gain among these genotypes. Among 139 line UNH105 segregants, B ²³ B ²³ hosts had significantly lower lesion scores than B ²⁴ B ²⁴ chickens. No other differences in immune response among line UNH105 genotypes were detected.     

MHC and Non-MHC genetic influences on rous sarcoma metastasis in chickens

The B ⁵/B ⁵ genotype, in Leghorns, was associated with a high degree of metastasis of Rous sarcoma virus-induced tumors, but in combination with a Leghorn-New Hampshire background markedly less metastasis occurred. Initially, four mating types were used: B ⁵/B ⁵ × B ⁵/B ⁵ chickens from the F₅ generation of the cross of Leghorn lines 6₁ and 15₁, B ²⁴/B ²⁴ × B ²⁴/B ²⁴ chickens from line UNH 105 (New Hampshires), and reciprocal crosses of B ⁵/B ⁵ × B²⁴/B²⁴ chickens. Subsequently, F₂ generation progeny of the cross of B⁵/B⁵ and B ²⁴/B ²⁴ breeders, as well as B ²⁴/B ²⁴ line UNH 105 and B ⁵/B ⁵ (6₁ × 15₁)F₂ chickens, were used. Six-week-old chickens were inoculated in the wingweb with Rous sarcoma virus. Chickens dying during a 10-week period after inoculation were necropsied and suspect metastatic lesions examined histologically. Among 234 terminal chickens from the initial four mating types the incidence of metastasis associated with B ⁵/B ⁵ Leghorns (66%) was substantially higher than for B ²⁴/B ²⁴ New Hampshires (12%) and B ⁵/B ²⁴ progeny of reciprocal Leghorn-New Hampshire crosses (19 and 24%). Subsequently, among 524 terminal hosts in the Leghorn-New Hampshire F₂ population, B genotype significantly influenced tumor dissemination. However, among 52 concurrently challenged B ⁵/B ⁵ hosts from the (6₁ × 15₁)F₂ population the incidence of metastasis (60%) was significantly higher than among 122 B ⁵/B ⁵ hosts from the Leghorn-New Hampshire F₂ population (31%), indicating a non-major histocompatibility complex genetic effect on metastasis.     

Increased growth of RSV-induced tumors in chickens partially tolerant to MHC alloantigens

Chickens withB ² B ² MHC genotypes were made partially tolerant to B₅ MHC cell-surface antigens and the fate of their Rous-sarcoma-virus (RSV)-induced tumors was determined.B ² B ² chickens partially tolerant to viable or lysed white blood cells (WBC) or viable red blood cells (RBC) fromB ⁵ B ⁵ chickens had a significantly higher incidence of tumor progression than untreated, PBS-treated, orB ² B ² chickens inoculated with WBC from otherB ² B ² chickens. The criteria for tolerance were absence of antibody titer to the cell type inoculated and acceptance of allografts fromB ⁵ B ⁵ donors byB ² B ² chickens. Graft-vs-host reactions occurred only inB ² B ² chickens inoculated with viable WBC fromB ⁵ B ⁵ chickens. It appears thatB ² B ² chickens partially tolerant to B₅ antigens failed to mount a successful immune response to RSV-induced tumors partly because a B₅ MHC antigen(s) cross-reacted with a tumor associated antigen(s) thereby severely limitingB ² B ² host recognition of the tumor as foreign. Since WBC and RBC cell-surface antigens appear to contribute similarly to the effect, theB-F- region of the MHC may be involved.     

Volatile Constituents from Baccharis spp. L. (Asteraceae): Chemical Support for the Conservation of Threatened Species in Uruguay

Chemical bioprospecting is an important tool for generating knowledge regarding local human‐threatened floras and for conservation management. For Baccharis L. (Asteraceae), several volatile components have been reported for Brazil, Argentina, Bolivia, and Chile as a result of bioprospection, but not for Uruguayan flora, which is composed of more than 50 native species. In this work, through collection of aerial parts of different species and volatile simultaneous‐distillation extraction and gas chromatography‐mass spectrometry analyses, twelve native species of Baccharis were studied (B. articulata, B. cultrata, B. genistifolia, B. gibertii, B. gnaphalioides, B. ochracea, B. phyteumoides, B. punctulata, B. crispa, B. dracunculifolia, B. linearifolia subsp. linearifolia, and B. spicata). A detailed analysis of the male and female volatile composition was conducted for the last four species. The profiles of B. cultrata, B. genistifolia, B. gibertii, and B. gnaphalioides are reported for the first time. Because half of the species analyzed in this work are in Uruguay and are threatened or potentially threatened by human economic activities, the importance of their conservation as natural, sustainable resources is highlighted.     

Genetic linkage between immune response to GAT and the fate of RSV-induced tumors in chickens

Recent studies suggest that the gene locus controlling the fate of tumors induced by Rous sarcoma virus (RSV) is linked to theB histocompatibility complex. Birds carrying the dominant allele regress the tumor; homozygous recessives being unable to do so, develop large tumors and die. These are called progressors.The Bryan strain of RSV was inoculated into 220 6 week old Leghorns homozygous forB ¹ B ¹,B ² B ², orB ¹⁹ B ¹⁹ of which the percentages of progressors were 79, 22 and 56, respectively. The balance of each were regressors and survived.TheB ¹ B ¹ test birds were derived from special matings, i.e., high and low immune responders to the amino acid polymer, GAT. Of 67 tests progeny of theB ¹ B ¹ GAT-low mating, 63 or 94% proved to be progressors, and 6% were regressors. Of 84 test progeny of theB ¹ B ¹ GAT-high matings, 67% were progressors, and 33% were regressors. The difference between the high and low GAT responders is highly significant and indicates that the locus controlling the fate of RSV-induced tumors is closely linked to the locus controlling immune response to GAT. The latter maps within theIr region of theB histocompatibility complex.     

Boron translocation in coffee trees

Boron deficiency in coffee trees (Coffea arabica) is widespread, however, responses to B fertilizer have been erratic, depending on the year, method, and time of application. A better understanding of B uptake, distribution, and remobilization within the plant is important in developing a rational fertilization program. Field and greenhouse experiments were conducted to study B distribution and remobilization in coffee trees. Boron was provided either in the nutrient solution or sprayed on the leaves of trees grown under adequate or transient B deficiency. There was clear evidence for B translocation via symplast (remobilization) to coffee grains, even in well-nourished plants. When ¹⁰B was present in the nutrient solution during most part of fruit filling, from 33 to 40% of the B found in coffee fruits was absorbed during this period, depending on the timing and duration of the B deficiency treatment. In the field, when B was sprayed once on the leaves, around 4% of the fruit B was derived from the foliar fertilizer. Boron remobilization within coffee trees is limited in well nourished plants, but it can be significant during periods of temporary B deficiency in plants otherwise well nourished with B. The implications of these findings for B fertilization practice, are discussed.     

The peptide binding specificity of HLA-B27 subtypes

Five HLA-B27 subtypes, B^*2701, B^*2703, B^*2704, B^*2705, and B^*2706, were tested for direct binding with twenty-six synthetic nonapeptides carrying the primary anchor residue motifs (combination of amino residues at positions 2 and 9) relevant to B^*2705. The peptide sequences were derived from human HSP89, P53 and MBP. The alpha chains were immunospecifically isolated from LH (B ^* 2701), CH (B ^* 2703), WE1 (B ^* 2704), BTB (B ^* 2705), and LIE (B ^* 2706) cells and their peptide binding was measured by the HLA class I alpha chain refolding assay. The data obtained indicated that the B27 subtypes tested can bind a common set of peptides carrying several different anchor residue motifs. The motifs, R-K and R-R, reported for B^*2705 and a new motif H-R were accepted by B^*2703, B^*2704, and B^*2706, but not by B^*2701. However, other motifs, including known B^*2702 and/or B^*2705 motifs, R-H, R-L, R-A, and R-F, and a new motif found here, R-G, were apparently accepted by all B27 subtypes tested. The observed cross-peptide binding in the B27 subgroup is compatible with the so-called arthritogenic peptide hypothesis in the pathogenesis of ankylosing spondylitis.     

GISH-based comparative genomic analysis in Urochloa P. Beauv.

The genus Urochloa P. Beauv. [syn. Brachiaria (Trin.) Griseb.] comprises species of great economic relevance as forages. The genomic constitution for the allotetraploid species Urochloa brizantha (cv. Marandu) and Urochloa decumbens (cv. Basilisk) and the diploid Urochloa ruziziensis was previously proposed as BBB¹B¹, B¹B¹B²B² and B²B², respectively. Evidence indicates U. ruziziensis as the ancestral donor of genome B² in U. decumbens allotetraploidy, but the origin of the genomes B and B¹ is still unknown. There are diploid genotypes of U. brizantha and U. decumbens that may be potential ancestors of the tetraploids. The aim of this study was to determine the genomic constitution and relationships between genotypes of U. brizantha (2x and 4x), U. decumbens (2x and 4x) and U. ruziziensis (2x) via genomic in situ hybridization (GISH). Additionally, chromosome number and genome size were verified for the diploid genotypes. The diploids U. brizantha and U. decumbens presented 2n?=?2x?=?18 chromosomes and DNA content of 1.79 and 1.44 pg, respectively. The GISH analysis revealed high homology between the diploids U. brizantha and U. decumbens, which suggests relatively short divergence time. The GISH using genomic probes from the diploid accessions on the tetraploid accessions’ chromosomes presented similar patterns, highlighting the genome B¹ present in both of the tetraploids. Based on GISH results, the genomic constitution was proposed for the diploid genotypes of U. brizantha (B¹B¹) and U. decumbens (B¹′B¹′) and both were pointed as donors of genome B¹ (or B¹′), present in the allotetraploid genotypes.

     

Role of the immune-response region of the B complex in the control of the graft-vs-host reaction in chickens

The relative importance of the B and IR regions of the chicken B complex were compared as to their role in the graft-versus-host (GVH) reaction. Spleen enlargement (splenomegaly) on 19-day-old embryos, inoculated 5 days earlier with immune competent leukocytes, served as the test for the GVH reaction. The B blood group locus was the marker of the B region, and the Ir-GAT gene was the marker of the immune response (Ir) region of the B complex, the major histocompatibility system (MHS) of chickens. The test stocks consisted of B¹B¹ GAT-Low (1-Low) and B¹⁹B¹⁹ Gat-High (19-High) birds of our S1 Leghorn line plus the recombinant genotypes B¹B¹ Gat-High (1-High) and B¹⁹B¹⁹ GAT-low (19-Low). A dosage of 0.1 ml of donor white blood cells was injected into each of 191 recipient embryos on day 14, and the spleens were removed and weighed on day 19. Of 16 combinations of (donor blood)-(host embryos), arranged with respect to the four genotypes listed above, four were compatible, e. g., (1-Low)-(1-Low). There were four incompatible combinations at the B locus, four at the GAT locus, and four at both the B and GAT loci. All 16 combinations were replicated. Results were expressed as a splenomegaly index (SI), that is, the ratio of incompatible to compatible spleen weights corrected for differences in embryo weight. If (SI-1) is greater than 0, the GVH reaction is considered positive within sampling errors. The mean (SI-1) indexes obtained were: incompatible at GAT-0.5±0.07; incompatible at B-1.34±0.10. Thus, both GAT and B contributed to the GVH reaction, but the B region was much stronger than the IR region. The results were strongly asymmetrical: maximal stimulation occurred when the host embryo was B¹⁹B¹⁹ GAT-high and donor leukocytes were B¹B¹ GAT-Low. The parental donor-host paired combinations gave stronger GVH reactions than did the recombinant pairs. Effects of incompatibilities at the two regions proved additive when compared with two-locus differences of parental genotypes. In general, the results proved that the IR region, as specifically defined by recombinants obtained in our S1 line of Leghorns, plays a significant, but minor, role in the GVH reaction compared with the region of the B complex identified with the B blood-group locus.     

Pollen morphology of six species of Bupleurum L. (Apiaceae) present in Sicily and taxonomic implications

Abstract

In this study, using light and scanning microscopes, the morphobiometric characters of pollen grains of Bupleurum fruticosum L., B. fontanesii Guss. ex Caruel, B. gerardi All., B. lancifolium Hornem., B. semicompositum L., B. tenuissimum L. have been analysed. The elaboration of qualitative and quantitative palynological data has allowed us to formulate a key of identification which characterizes six morphotypes. Pollen grains of B. fruticosum (a perennial species) have been distinguished from the grains of the other annual species examined by us on the basis of several morphobiometric characters, a condition which has confirmed the systematic arrangements suggested by several authors. The close palynological affinity between B. tenuissimum and B. semicompositum compared with B. gerardi has supported the placement of these three species in a distinct subsect. of the sect. Eubupleura Briq. or in a distinct subsect. of the sect. Isophyllum (Hoffm.) Dumort. Similarly, our palynological data on B. fontanesii have confirmed the systematic arrangement. However, these data differ from those reported by different authors who placed the three species in the sect. Aristata Godron subsect. Juncea Briq.     

亚热带区4种林地土壤微生物生物量碳氮磷及酶活性特征

在位于亚热带丘陵区的长沙县大山冲林场选取地域毗邻、环境条件(立地、土壤、气候)基本一致的杉木人工林(CL)和3种次生林:马尾松-柯(又名石栎)针阔混交林(PM-LG)、南酸枣落叶阔叶林(CA)、柯-青冈常绿阔叶林(LG-CG),每种林地随机设置5个20 m×20 m的样地,分别采集表层(0—15 cm)和亚表层(15—30 cm)土壤样品,测定土壤微生物生物量碳(B_C)、氮(B_N)、磷(B_P)和蔗糖酶(INV)、脲酶(URE)、酸性磷酸酶(ACP)、过氧化氢酶(CAT)活性,分析4种林地土壤微生物生物量和酶活性及其与土壤化学性质的关系。结果表明:表层和亚表层土壤B_C、B_N、B_P和ACP活性依次为:CA LG-CG PM-LG CL,INV和URE活性依次为:LG-CG CA PM-LG CL,CAT活性依次为:CA PM-LG LG-CG CL,说明森林植被恢复对土壤微生物生物量和酶活性有明显的促进作用。通径分析表明,土壤B_C、B_N、B_P的直接影响因素和主要影响因素分别为SOC和TN/TP,TN和TN/TP,TP和SOC/TP,而TN/TP与B_C之间,TN与B_N之间具有较强的负相关;INV、ACP活性的直接影响因素主要是TN、TN/TP,其中TN/TP与INV、ACP活性具有较强的负相关;URE、CAT活性分别为B_P/TP和B_P,B_C/SOC和SOC,其中B_P与URE活性具有较强的负相关,B_C/SOC、SOC两者与CAT活性具有较强的正相关。此外,土壤B_C、B_N、B_P以及INV、URE、ACP、CAT活性的剩余余项通径系数较低,说明土壤化学性质对土壤微生物生物量,以及土壤化学性质和微生物生物量对土壤酶活性具有较大的影响。土壤B_C、B_N、B_P之间及其与土壤酶活性呈显著正相关。     

Molecular analysis of HLA-B39 subtypes

Serological studies have suggested the presence of a new HLA-B39 subtype (B39.2) in the Japanese population. To identify the new HLA-B39 subtype and compare it with an other HLA-B39 subtype (B39.1), the genes encoding HLA-B39.1 (B ^* 39013) and B39.2 (B ^* 3902) have been cloned from Japanese. We have sequenced these genes and completed the sequence of HLA-B39.1 (B ^*39011 ) gene from a Caucasian that was partially sequenced. Comparison of the sequence data revealed that B ^* 3902 and B ^* 39013 differ by three nucleotide substitutions which result in a two amino acids change at residues 63 and 67, while one silent substitution at codon 312 is found between B ^* 39011 and B ^* 39013. These results suggest that B ^* 3902 has evolved from B ^* 39013 rather than B ^* 39011.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession numbers M94051 (HLA-B^*39013), M94052 (HLA-B^*39011), and M94053 (HLA-B^*3902).     

Class II MHC cDNAs in 15I5 B-congenic chickens

 cDNA was obtained from the bursae of Fabricius of chickens from six B-congenic lines developed at this laboratory and studied for expression of class II B-LB genes. Following cDNA amplification, cloning and sequencing, genes were assigned to B-LB loci based on characteristic DNA sequences, amino acid relatedness to characterized genes, and level of expression. Genes from the B-LBI, B-LBII, and B-LBVI loci were differentially expressed in chickens with the B ² , B ⁵ , B ¹³ , B ¹⁵ , or B ²¹ haplotypes. Chickens of all haplotypes expressed a B-LBII gene. Additional B-LB genes expressed included: B-LBI genes in the B ⁵ and B ¹⁹ haplotypes; a B-LBI/VI recombinant gene in the B ² haplotype; and a B-LBVI gene in the B ¹³ haplotype. The B-congenic lines have demonstrable differences in resistance to Marek’s disease (MD), and in responses to MD viral vaccines. This variability in disease resistance may be correlated with polymorphisms in the expressed B-LB genes, or with differential expression of genes at different loci. Received: 18 April 1997 / Revised: 29 September 1997     

Comparison of mitochondrial genomes provides insights into intron dynamics and evolution in Botryosphaeria dothidea and B. kuwatsukai

Botryosphaeria dothidea is one of the most common fungal pathogens on a large number of hosts worldwide. Botryosphaeria dothidea and B. kuwatsukai are also the main causal agents of apple ring rot. In this study, we sequenced, assembled and annotated the circular mitogenomes of 12 diverse B. dothidea isolates (105.7–114.8 kb) infecting various plants including apple, and five diverse B. kuwatsukai isolates (118.0–124.6 kb) from apple. B. dothidea mitogenomes harboured a set of 29–31 introns and 48–52 ORFs. In contrast, B. kuwatsukai mitogenomes harboured more introns (32–34) and ORFs (51–54). The variation in mitogenome sizes was associated mainly with different numbers of introns and insertions of mobile genetic elements. Interestingly, B. dothidea and B. kuwatsukai displayed distinct intron distribution patterns, with three intron loci showing presence/absence dynamics in each species. Large numbers of introns (57% in B. dothidea and 49% in B. kuwatsukai) were most likely obtained through horizontal transfer from non-Dothideomycetes. The mitochondrial gene phylogeny supported the differentiation of the two species. Overall, this study sheds light into the mitochondrial evolution of the plant pathogens B. dothidea and B. kuwatsukai, and intron distribution patterns could be useful markers for studies on population diversity.     

TheB locus (MHC) in the chicken: Association with the fate of RSV-induced tumors

The fate of tumors induced by Rous sarcoma virus (RSV) was determined in anF ₂ population segregating at three alloantigen loci. TheF ₁ resulted from crossing tumor-resistant RPRL line 6₁ (B ² B ² D ³ D ³ I ² I ²) with tumor-susceptible RPRL line 15₁ (B ⁵ B ⁵ D ⁴ D ⁴ I ⁸ I ⁸). Among theF ₂ segregantsB ² B ²,B ² B ⁵, andB ⁵ B ⁵, the percentage of chicks dying of terminal tumors (by 70 days post-inoculation) was 5, 26, and 93, respectively (P0.01). NeitherD orI genotypes nor sex significantly affected tumor growth. In chickens with terminal tumors, the incidence of metastatic lesions was also significantly associated withB genotypes. Thus, the MHC chromosomal region in the chicken appears to exert a crucial role in determining the outcome of RSV-induced tumors.     

A three-locus model for the chicken major histocompatibility complex

The major histocompatibility complexes (B complexes) of chickens of various origins have been studied by serological and biochemical methods. TwoB complexes are of particular interest:B ^R1, a recombinant haplotype derived from theB complexes of the inbred CB and CC strains, andB ^G-B1 , theB haplotype of the G-B1 strain. TheB ^R1 haplotype differs detectably from theB ^CB haplotype only at a locus controlling the synthesis of an antigen, B-G, which (in peripheral blood) is present only on red cells. Anti-B-G sera precipitate, from¹²⁵I-labeled red cell lysates, two chains of apparent molecular weights 42,000 and 31,000 (measured under reducing conditions); the smaller is perhaps derived by proteolysis from the larger. TheB ^G-B1 haplotype differs detectably from theB ^CC haplotype only at a locus controlling the synthesis of an antigen whose tissue distribution and biochemical and biological properties are identical to those of B-G. The chicken major histocompatibility complex therefore contains at least three loci—those controlling synthesis of the B-G, and of the previously defined B and B-L antigens.The following abbreviations are used in this paper MHC major histocompatibility complex - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis - MLR mixed leukocyte reaction - GVH graft-versus-host reaction