Specific Biological Effects of an Anti‐Rat PMN Antiserum Intraperitoneally Injected into F344/N Rats

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Abstract
Neutropenia can be produced with antimitotic chemicals, but this method lacks specificity. An alternative is to use antibody‐dependent cytotoxicity to produce neutropenia; however, this method has not been completely evaluated with respect to efficacy, specificity, and potential collateral damage, especially to constituents of bone marrow. This study used in vitro and in vivo methods to evaluate specific biological effects of a commercially available rabbit anti‐rat neutrophil (PMN) antiserum in F344/N rats. The viability of rat pulmonary alveolar macrophages (PAMs), PMNs, and lymphocytes in vitro was quantified using a trypan blue dye exclusion test. Amounts of antiserum in vitro that rendered PMNs 100% nonviable did not decrease the viability or phagocytic ability of the PAMs and did not decrease the viability of the lymphocytes. Intraperitoneal (IP) injection of the antiserum into rats resulted in complete depletion of the PMNs and about a 50% depletion of the lymphocytes in circulating blood within 24 hours. The numbers of both cell types remained lowered for 5 days, but returned to control values by Day 6 after the IP injection. The antiserum had no effect on the numbers of PAMs or lymphocytes in the pulmonary alveolar airspaces, as determined by quantifying the numbers of these cell types in bronchoalveolar lavage fluid (BALF). The numbers of PMNs in BALF, however, decreased on Days 3 and 4 after IP injection of antiserum, but were not different from control values by Day 5. The viability of the PAMs in BALF of treated rats was not different from control values at any time point. There were no morphological indications that the injected antiserum damaged lung tissue or stem cells in bone marrow. Results demonstrate that the anti‐rat PMN antiserum administered IP to F344/N rats depletes circulating PMNs and partially depletes lymphocytes for a period of about 6 days without adversely affecting the precursors of red or white blood cells in bone marrow. We concluded that the antiserum is a relatively specific way to temporarily render rats neutropenic without damaging precursor cells in bone marrow.