Identification of two antigenically and genetically distinct lineages of H3N8 equine influenza virus in Sweden.

Four Swedish strains of equine H3N8 influenza virus isolated from outbreaks during the last 4 years were characterized. Antigenic typing using monoclonal antibodies raised against a variety of H3N8 strains showed that the viruses are heterogeneous, the 1993 isolate being closely related to the 1991 Swedish isolate TAB/91 and the other three isolates from 1994 and 1996 being more closely related to each other. This pattern is reflected in the phylogenetic data calculated from nucleotide sequencing of the haemagglutinin genes. H3N8 equine influenza can be seen to be evolving in two distinct lineages, one European and one American. The 1993 isolate is closely related to the European lineage and is the most recent Swedish strain of this lineage to be isolated. The 1994 and 1996 isolates fit into the American lineage, which contains recent isolates from the United States and also Britain. These results indicate that American-type H3N8 viruses have become endemic in Sweden and, in light of the antigenic differences which can be observed between viruses belonging to the two lineages, we believe that equine influenza virus vaccines should be updated with an American-type virus strain.

Neutralizing cross-reactive and non-neutralizing monoclonal antibodies to HIV-1 gp120.

Amino acid sequences inducing neutralizing antibodies to HIV-1 were sought. Murine monoclonal antibodies (MAbs) were characterized by their reactivity with the envelope precursor gp160 or the Escherichia coli recombinant DNA products pB1 and pE3 representing the carboxy- and amino-terminal halves of mature envelope gp120. Fine mapping of the MAb determinants was performed using defined 15-mer synthetic peptides spanning the entire envelope gp120 region of HIV-1. One group of MAbs recognizes epitopes (amino acids 304-323) occurring in a small region with variable and conserved amino acid sequences of gp120. These MAbs mediate neutralization of the HIV-1 strain HTLV-IIIB (HIV-1IIIB) which was used for immunization. Nine out of 11 primary HIV-1 isolates were neutralized well or moderately well. In addition, prominent serological reactivity was noted with peptide sequences of strains of various European or American origins, but not with two HIV-1 strains of African origin. The cross-reactivity contrasts with previously described type-specific reactions to other sequences of this region. The reactivity to the short conserved site GPGR with its flanking amino acids may explain the broad sequence cross-reactivity seen with our neutralizing MAbs. Two other MAbs recognize conserved epitopes (amino acids 79-103) situated in the amino-terminal region of gp120. These MAbs did not neutralize HIV-1IIIB.