Abstract
Immunogenicity, eliciting antigenicity and cross-reactivity of new cephem antibiotics, BMY-28100 and cefepime, were studied by means of passive cutaneous anaphylaxis (PCA), passive hemagglutination (PHA) and active systemic anaphylaxis in guinea pigs, and of PCA in mice and the results were compared with those obtained with reference antibiotics. In addition, the direct COOMBS' reaction of the human blood was examined in vitro for the test antibiotics as compared with reference antibiotics. The results obtained are summarized as follows:
1. Immunogenicity
Immunogenicity of unconjugated antibiotics was examined using the corresponding conjugates with bovine γ-globulin (BGG) as eliciting antigen. When used as emulsions with FREUND'S complete adjuvant, cephalothin (CET) and benzylpenicillin (PCG) produced IgG1 and IgM antibodies in guinea pigs. However, cefepime as well as cephalexin (CEX) did not produce these antibodies, and BMY-28100 showed slightly active sensitization only for anaphylactic shock. In BALB/c and C3H/He mice, BMY-28100 and cefepime failed to produce antibodies under the experimental condition while IgE antibody formation to CET was observed.
2. Eliciting antigenicity
Unconjugated CET and PCG provoked anaphylactic signs in guinea pigs sensitized with their conjugates with rabbit serum albumin (RSA). Cefepime, however, provoked no anaphylactic shock and BMY-28100 as well as CEX showed slight signs. In the other systems examined, no reactions were observed when elicited with BMY-28100, cefepime or the reference antibiotics.
3. Immunological cross-reactivity
BMY-28100 did not cross-react with the reference antibiotics. While the antiserum to the RSA conjugate of CET provoked weak cross-reaction on PHA with the BGG conjugate of cefepime, the antiserum to the RSA conjugate of cefepime failed to react with the BGG conjugate of CET. Other cross-reactivities of cefepime were not observed against the reference antibiotics.
4. In vitro direct CoomBs' reaction
BMY-28100 did not induce the COOMBS' reaction of the human blood in vitro at the testable concentration of 10 mg/ml. Cefepime or cefazolin (CEZ) caused no reaction even at a high concentration of 80 mg/ml, while CET and PCG caused a positive reaction at 10-40 mg/ml and 60 mg/ml, respectively.
As shown above, immunogenicity and eliciting antigenicity of BMY-28100 and cefepime were somewhat weaker than CET and PCG but similar to CEX, and cross-reactivities of the test antibiotics with these reference antibiotics were not observed in general. The ability of BMY-28100 to give a positive reaction in the COOMBS' test was weaker than that of CET, and that of cefepime was weaker than CET and PCG and equivalent to CEZ.
From these results, it was concluded that BMY-28100 and cefepime were immunologically rather inactive under the experimental conditions.
