CHARACTERIZATION OF MONOCLONAL-ANTIBODIES THAT RECOGNIZE COMMON EPITOPES LOCATED ON O-ANTIGEN OF LIPOPOLYSACCHARIDE OF SEROTYPE-1, SEROTYPE-9 AND SEROTYPE-11 OF ACTINOBACILLUS-PLEUROPNEUMONIAE

Seven murine monoclonal antibodies (mAbs) against serotype 1 of Actino bacillus (Haemophilus) pleuropneumoniae (reference strain Shope 4074) were produced and characterized. All hybridomas secreting mAbs were re active with whole-cell antigens from reference strains of serotypes 1, 9 and 11, except for mAb 5D6 that failed to recognize serotype 9. The y did not react with other taxonomically related Gram-negative organis ms tested. The predominant isotype was immunoglobulin (Ig) M, although IgG(2a), IgG(2b) and IgG(3) were also obtained. The epitopes identifi ed by these mAbs were resistant to proteinase K treatment and boiling in the presence of sodium dodecyl sulfate and reducing conditions; how ever, they were sensitive to sodium periodate treatment. Enhanced chem iluminescence-immunodetection assay showed that mAbs could be divided in two groups according to the patterns of immunoreaction observed. Gr oup I (mAbs 3E10, 4B7, 9H5 and 11C3) recognized a ladder-like banding profile consistent with the O antigen of lipopolysaccharide (LPS) from smooth strains. Group H (mAbs 3B10 and 9H1) recognized a long smear o f high molecular weight which ranged from 60 to 200 kDa. The mAbs were tested against 96 field isolates belonging to serotypes 1, 5, 9, 11 a nd 12, which had previously been classified by a combination of serolo gical techniques based on polyclonal rabbit sera (counterimmunoelectro phoresis, immunodiffusion and coagglutination). The panel of mAbs iden tified all isolates of serotypes 9 and 11, but only 66% of those belon ging to serotype 1. This may suggest the existence of antigenic hetero geneity among isolates of A. pleuropneumoniae serotype 1. These mAbs r eacted with epitopes common to serotypes 1, 9 and 11 of Actinobacillus pleuropneumoniae which were located on the O antigen of LPS.