Amino Acids in Hemagglutinin Antigenic Site B Determine Antigenic and Receptor Binding Differences between A(H3N2)v and Ancestral Seasonal H3N2 Influenza Viruses

ABSTRACT Influenza A H3N2 variant [A(H3N2)v] viruses, which have caused human infections in the United States in recent years, originated from human seasonal H3N2 viruses that were introduced into North American swine in the mid-1990s, but they are antigenically distinct from both the ancestral and current circulating H3N2 strains. A reference A(H3N2)v virus, A/Minnesota/11/2010 (MN/10), and a seasonal H3N2 strain, A/Beijing/32/1992 (BJ/92), were chosen to determine the molecular basis for the antigenic difference between A(H3N2)v and the ancestral viruses. Viruses containing wild-type and mutant MN/10 or BJ/92 hemagglutinins (HAs) were constructed and probed for reactivity with ferret antisera against MN/10 and BJ/92 in hemagglutination inhibition assays. Among the amino acids that differ between the MN/10 and BJ/92 HAs, those in antigenic site A had little impact on the antigenic phenotype. Within antigenic site B, mutations at residues 156, 158, 189, and 193 of MN/10 HA to those in BJ/92 switched the MN/10 antigenic phenotype to that of BJ/92. Mutations at residues 156, 157, 158, 189, and 193 of BJ/92 HA to amino acids present in MN/10 were necessary for BJ/92 to become antigenically similar to MN/10. The HA amino acid substitutions responsible for switching the antigenic phenotype also impacted HA binding to sialyl receptors that are usually present in the human respiratory tract. Our study demonstrates that antigenic site B residues play a critical role in determining both the unique antigenic phenotype and receptor specificity of A(H3N2)v viruses, a finding that may facilitate future surveillance and risk assessment of novel influenza viruses. IMPORTANCE Influenza A H3N2 variant [A(H3N2)v] viruses have caused hundreds of human infections in multiple states in the United States since 2009. Most cases have been children who had contact with swine in agricultural fairs. These viruses originated from human seasonal H3N2 viruses that were introduced into the U.S. swine population in the mid-1990s, but they are different from both these ancestral viruses and current circulating human seasonal H3N2 strains in terms of their antigenic characteristics as measured by hemagglutination inhibition (HI) assay. In this study, we identified amino acids in antigenic site B of the surface glycoprotein hemagglutinin (HA) that explain the antigenic difference between A(H3N2)v and the ancestral H3N2 strains. These amino acid mutations also alter binding to minor human-type glycans, suggesting that host adaptation may contribute to the selection of antigenically distinct H3N2 variants which pose a threat to public health.

Inter- and interspecific serological relationships in Pellia epiphylla complex

Antigenic proteins were used as markers for the study of relationships between three liverwort species from <em>P. epiphylla</em> complex. It has recently been shown that the electrophoretic phenotypes of this species suggested an amphiploid origin of <em>P. borealis</em>. Two sibling species: <em>P. epiphylla</em> -species S and -species N could have probably represented the parental species for <em>P. borealis</em>. We examined three clones of <em>P. borealis</em> from different localities using immunodiffusion. Then we compared them with <em>P. epiphylla</em> species S and N as well as with the mixture of proteins of <em>P. epiphylla</em> S and N samples. The results indicate that polyploid <em>P. borealis</em> shows an identical immunological pattern to that of the mixture of proteins of putative parental species. Only in one case the result resembled much more the pattern of <em>P. epiphylla</em> S proteins. The sibling species <em>P. epiphylla</em> S and N showed antigenic difference but the nature of the differences requires further studies. Antigenic pro-perties of proteins from <em>P. epiphylla</em> S and N and of their allopolyploid - <em>P. borealis</em>, indicated some specifity of the protein spectrum in each of the parental species and intermediate character of proteins in the polyploid forms.

Distinct IGHV Repertoire Features In Chinese Chronic Lymphocytic Leukemia Patients

Mounting evidence indicates that immunoglobulin variable heavy-chain (IGHV) repertoire and mutational status in chronic lymphocytic leukemia (CLL) patients are prognostically relevant. However, rare data is available in Chinese CLL population. Our group investigated 270 Chinese CLL patients for their IGHV sequences and discovered significant differences between Chinese and European CLL patients. First of all, 169 (62.6%) patients in our group got mutated IGHV and 101 (37.4%) were unmutated, rendering a considerable higher percentage of mutated subgroup compared with European patients (55%) (Figure 1). While IGVH3 is still the most frequently used IGVH gene in Chinese CLL patients (135/270, 50%), discrepancy occurs in the usage of IGVH1 gene, which only presents in 13.7% (37/274) patients in our cohort whereas 23.79% for European (Figure 2). Regarding IGHV subgroups, IGHV3-23 and IGHV4-34 are more often used in Chinese CLL patients (10.7% and 10.4%, respectively). Remarkably, IGHV1-69, the most prevalent IGHV subgroup in European CLL patients (12.81%), only accounts for 5.2% (14/270) Chinese cases.Figure 1Higher percentage of mutated IGHV in Chinese CLL patientsFigure 1. Higher percentage of mutated IGHV in Chinese CLL patientsFigure 2Different IGHV gene usage between Chinese and European CLL patients, with IGVH1 gene accounts for 23.79% of European CLL patients and for only 13.70% of Chinese CLL patients.Figure 2. Different IGHV gene usage between Chinese and European CLL patients, with IGVH1 gene accounts for 23.79% of European CLL patients and for only 13.70% of Chinese CLL patients.Figure 3IGVH1-69 is the most prevalent IGHV gene among European CLL patients(12.81%), however, only 5.20% Chinese CLL patients use VH1-69. IGVH4-39 and IGVH4-59 are more often used in Chinese CLL patients (7.80% vs 3.73% and 5.60% vs 2.75%, respectively).Figure 3. IGVH1-69 is the most prevalent IGHV gene among European CLL patients(12.81%), however, only 5.20% Chinese CLL patients use VH1-69. IGVH4-39 and IGVH4-59 are more often used in Chinese CLL patients (7.80% vs 3.73% and 5.60% vs 2.75%, respectively). We further studied the distribution of stereotyped BCR in our cohort. Thirty-eight patients (14.07%) with stereotyped BCR that belonged to 21 subsets were identified, with 1 to 7 sequences contained each. Among them, subset 1 and subset 8 are the most common types with 6 and 7 cases respectively. Three new subsets were discovered (Table 1). Notably, only 1 case belonged to subset 2, the subset with largest group size in western world. Hence, we conclude that Chinese CLL patients show unique IGHV repertoire features compared to patients from western countries. While the mechanism within remains unknown, the discrepancy might due to antigenic difference in geographically remote areas.Table 1Three new subsets of BCR stereotypy in Chinese CLL patientsNO.IGHVIGHDIGHJM/UMIdentityHCDR3 AA sequenceLengthNovel 1NJ-15IGHV4-59*083-22*016*03UM100,00%ARGNYYDSSGYYYVGYYYYYMDV23NJ-31IGHV4-59*013-22*016*03UM99,65%ARGDYYDSSGYYYVGYYYYYMDV23Novel 2NJ-186IGHV3-23*013-22*014*02M96.60%AKGYRDNYDGDQSSVFDS18NJ-23IGHV3-23*012-21*014*02M96,53%AKGYRDNYDGDQSSVFDS18Novel 3NJ-36IGHV4-34*016-6*015*02M93,33%AKLMAGRPNWFDP13NJ-123IGHV4-34*016-6*015*02M91,67%AKLMAGRPNWFDP13 Disclosures: No relevant conflicts of interest to declare.

Bacteriophage MAV1 Is Not Associated with Virulence of Mycoplasma arthritidis

ABSTRACT Previous studies demonstrated that Mycoplasma arthritidis strain 158 acquired a high degree of virulence upon lysogenization with bacteriophage MAV1. In the present study, the association between MAV1 and virulence was reexamined by creating new lysogens of 158 and of a relatively avirulent mutant, strain 158-1. In the absence of lysogenization, 158 was more virulent than expected. The virulence of 158 and 158-1 did not increase upon lysogenization. A major antigenic difference between 158 and 158-1 was identified that is unrelated to MAV1 and could account for the difference in virulence.