Agents and Actions, vol. 16, 1/2 (1965) 0065-4299/85/020015-0251.90 9 1985 Birkh~iuserVerlag, Basel Extravasation of proteins in the joint tissue: differential behaviour of native BSA and cationic mBSA JAN WILLEM LENS, 1 WIM B. VAN DEN BERG, LEVINUS B.A. VAN DE PUTTE and WIL A. ZWARTS University Hospital St Radboud, Department of Rheumatology, Nijmegen, The Netherlands Summary Mice were intravenously injected with I~SI-labelled native BSA and cationic mBSA. The amount of 1251-protein in the extra- and intravascular compartment was determined in normal joints and in joints in which the vascular permeability was increased by histamine. The extravasation of BSA and mBSA is different. More BSA compared with mBSA accumulated in normal joints and the extravasation of BSA increased almost 3 times shortly after histamine injection, whereas histamine hardly affected the extra- vasation of mBSA. Introduction Intravenous injection of homologous antigen (mBSA = methylated bovine serum albumin) in mice with unilateral chronic mBSA-induced joint inflammation causes a flare-up of the chronic arthritis without affecting the contralateral non-arthritic joint [1]. In addition to the presence of local hyper-reaetivity in the chronically-inflamed joint [2] an important principle may be the increased leakage of mBSA into the arthritic joint. Extravasation of radiolabelled albumin has been thoroughly studied in the skin [3, 4] but only scant data are available in the joint [5, 6],We examined the accumulation of i.v.-injected radiolabelled native bovine serum albumin (BSA) and positively charged (cationic) mBSA in normal and histamine treated knee joints. Whole knee joints were removed and the proportion of ~zs I antigen in the joint blood volume and in the bone marrow as compared with the total count rate was determined. Methods Mice (C57B1) weighing 25-27 g were intravenously injected with 100/2g 1z~I-BSA. 51Cr-labelled autologous red blood cells (5~Cr-RBC) were added to determine the blood volume. This method can not be used in experiments with 125I-mBSA since addition of this cationic antigen causes agglutination of the RBC. Immediately after antigen ad- ministration the animals received an intra-articular (i,a.) injection with histamine (6 /2g) in the right knee joint and saline in the left. Knee joints were removed in toto by cutting the femur and tibia at sites adjacent to the joint cavity, and the count rate of 115I and 5iCr was measured by gamma- counting. A blood sample (20/21) was taken from the orbital plexus immediately before sacrifice and the count rate of IzSI-BSA and 51Cr-RBC per ml blood determined. These values and the total 51Cr-RBC counts in the joint can be used to calculate the joint blood volume and the amount of I/5I-BSA in this volume. In addition, the bone marrow was removed from the open ends of the tibia and femur by flushing with saline. 1Correspondence: Dr J.W. Lens, University Hospital St Radboud, Department of Rheumatology, Geert Grooteplein Zuid 8, 6525 GA Nijmegen, The Netherlands. Results and discussion The figure shows the count rate of 12~I-BSA and 51Cr-RBC in total joints at various times after injection of histamine into the right knee joint and saline in the left. The count rate is increased at 5 min after histamine injection, reaches a maximum after 10 rain and is still increased after 30 rain. The count rate is unchanged in the contralateral knee joint injected with saline. No change is observed in the 5~Cr-RBC count rate indicating that the joint blood volume (approximately 5 /21) is unaltered after histamine or saline injection in the joint. In this experiment the accumulation of t2Sl-BSA was measured in the total joint which includes the amount of 1zSI-BSA not only in the extravascular synovial tissue but also in the blood and in the bone marrow. In the table the measurements of I~SI-BSA are corrected for the amount of 1zSI-BSA in the joint blood volume and the amount of 12SI-BSA in the bone marrow of tibia and femur. The measurements are expressed as percentage of the administered dose. In a saline injected knee joint 0,51% of the administered dose is found in the joint but 0.16%, i.e. a third part, is present in the joint blood volume. When the values in the right histamine injected and left saline injected joint are corrected for this intravascular part, the R/L ratio, which reflects the increase in extravasation after histamine treatment, increases from 2.2 to 2.7 (see table). After removal of the bone marrow the values were further reduced by about 20%, but the R/L ratio was not significantly altered (see table). 6000 5000 c 4000 E 3000 = 2000 1000 Figure IzsI_BS A ""~'~ ~ 1251-BSA (R) 9 12Sl- BSA(L) , , :~(R) Cr- RBC r2 5 10 30 time(min) after i.a. injection and 51Cr-RBC counts in right knee joint (R) injected with histamine (6 /2g) and in left knee joint (L) injected with saline. Values represent mean of 3 joints. Mice were intravenously injected with 100/2g 125I-BSA (500,000 c.p.m.) and 51Cr-RBC (16,000 c.p,m.) in 0.2 ml saline.