Effects of systemic complement activation on renal circulation of rats

Differences in cortical microcirculation in the kidneys of unilaterally congenital hydronephrotic rats

The surgically induced split hydronephrotic kidney has been generally accepted as a valid model for the assessment of renal microcirculation by means of intravital microscopy. Whereas nearly all previous work on this issue has been done with a transillumination technique, we used an epiillumination model that is suitable for investigation of microvascular perfusion in both normal and hydronephrotic kidneys without surgical manipulation of the ureter. By means of the congenital unilaterally hydronephrotic Tauchi rat, microcirculation of the hydronephrotic and that of the nonhydronephrotic kidney were compared. For that purpose both the hydronephrotic and the nonhydronephrotic kidneys of Tauchi rats were exteriorized on a specially designed microscopy stage. After injection of FITC-dextran and rhodamine 6G, microvascular perfusion was assessed in both kidneys. The new model allowed visualization of arterioles, capillaries, and postcapillary venules in both the hydronephrotic and the nonhydronephrotic kidneys. Glomeruli could only be regularly seen in the hydronephrotic kidney, but also in some normal kidneys. Capillary blood cell velocity was significantly higher in the hydronephrotic kidneys (0.67 +/- 0.03 mm/s) compared to the normal kidney (0.32 +/- 0.05 mm/s; P < 0.05), whereas capillary diameters were smaller (4.2 +/- 0.02 microm vs. 5.7 +/- 0.2 microm; P < 0.05). In addition, the hydronephrotic kidney showed a significantly lower density of perfused microvessels compared to the normal controls. Epiillumination intravital microscopy allows assessment of the cortical microcirculation in both the hydronephrotic and the nonhydronephrotic kidneys without surgical induction of hydronephrosis. The hydronephrotic kidney shows significant microcirculatory differences compared to normal kidneys that should be taken into account when using a hydronephrotic model for pharmacological testing.

Frequent expression of complement resistance factors CD46, CD55, and CD59 on gastrointestinal cancer cells limits the therapeutic potential of monoclonal antibody 17-1A

BACKGROUND

One reason for the failure of monoclonal antibody (mab) trials in most cancer patients might be the presence of complement resistance factors that inhibit complement dependent cytotoxicity (CDC) and the release of inflammatory mediators (e.g., anaphylatoxins).

METHOD

We have determined the expression of CD46, CD55, and CD59 in five gastric, three colon, and seven pancreatic human cancer cell lines by immunostaining. The complement activating properties of mabs and conjugates with cobra venom factor (CVF) were studied in a 51Cr-release toxicity assay and in an ELISA to determine the release of C3a.

RESULT

Virtually all tumor cell lines strongly expressed CD46, CD55, and CD59, except KATOIII gastric cancer cells (CD55 and CD59 negative). In accordance with other studies we could confirm that expression of CD55 and CD59 inhibits a complement activation by mabs. Whereas 17-1A was able to induce a cytotoxic complement activation on KATOIII cells, neither a CDC nor an anaphylatoxin release (C3a) was observed on MKN28 cells (strong expression of CD55 and CD59). Conjugation with CVF, a strong activator of the alternative pathway of complement, could partially restore the complement activation by mabs. A 17-1A-CVF conjugate, although still nontoxic, induced the release of the anaphylatoxin C3a on both cell lines. The same observations were made in PancTuI pancreatic cancer cells treated with a conjugate of the mab CA19-9 and CVF.

CONCLUSIONS

Our study shows that complement resistance is a frequent event in gastrointestinal cancer, limiting the potential of monoclonal antibodies. Mabs, when conjugated with CVF, partially retain complement activating properties by releasing C3a, which in vivo will support a cellular immune response.